SEARCH · PubMed Health

Results for “Transfer”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6Linked to original sources

PubMed2003

Human seminal plasma displays significant phospholipid transfer activity due to the presence of active phospholipid transfer protein.

The lipid composition of germ cell membranes is considerably modified during spermatogenesis, sperm maturation and capacitation. Some of these modifications are caused by exchanges between soluble lipid donors or acceptors and cell membranes. The aim of this study was to assess whether significant lipid transfers between lipoprotein structures are detectable in human seminal plasma. Phospholipid and cholesteryl ester (CE) transfer activities were measured by specific fluorescence and isotopic assays. Seminal plasma samples did not display significant CE transfer. Substantial levels of phospholipid transfer activity were detected in all samples studied, levels were approximately 25% of the phospholipid transfer activity measured in human blood plasma. Concordantly, CE transfer protein was not detected in seminal plasma, while the presence of the phospholipid transfer protein (PLTP) was confirmed by Western blot analysis. Enzyme-linked immunosorbent assay indicated that seminal PLTP concentrations represented 25% of the concentration measured in blood plasma. Blockade of phosphatidylcholine and phosphatidyl-ethanolamine transfer by a 60 min, 56 degrees C heating step or with anti-PLTP antibody revealed that PLTP accounts for almost 80% of the phospholipid transfer activity present in seminal plasma. As shown by gel-permeation chromatography and Western blot analysis, seminal PLTP activity was partially associated with prostasomes. Significantly higher PLTP activity levels were measured in seminal plasma samples with low seminal vesicle secretions. The latter observation may reflect the sustained secretion of active PLTP that is diluted in a variable volume of PLTP-free seminal vesicle secretion. In conclusion, human seminal plasma displays significant phospholipid transfer activity due to the presence of active PLTP.

Carrier Proteins↗

PubMed2006

Validation of the Provincial Transfer Authorization Centre database: a comprehensive database containing records of all inter-facility patient transfers in the province of Ontario.

BACKGROUND: The Provincial Transfer Authorization Centre (PTAC) was established as a part of the emergency response in Ontario, Canada to the Severe Acute Respiratory Syndrome (SARS) outbreak in 2003. Prior to 2003, data relating to inter-facility patient transfers were not collected in a systematic manner. Then, in an emergency setting, a comprehensive database with a complex data collection process was established. For the first time in Ontario, population-based data for patient movement between healthcare facilities for a population of twelve million are available. The PTAC database stores all patient transfer data in a large database. There are few population-based patient transfer databases and the PTAC database is believed to be the largest example to house this novel dataset. A patient transfer database has also never been validated. This paper presents the validation of the PTAC database. METHODS: A random sample of 100 patient inter-facility transfer records was compared to the corresponding institutional patient records from the sending healthcare facilities. Measures of agreement, including sensitivity, were calculated for the 12 common data variables. RESULTS: Of the 100 randomly selected patient transfer records, 95 (95%) of the corresponding institutional patient records were located. Data variables in the categories patient demographics, facility identification and timing of transfer and reason and urgency of transfer had strong agreement levels. The 10 most commonly used data variables had accuracy rates that ranged from 85.3% to 100% and error rates ranging from 0 to 12.6%. These same variables had sensitivity values ranging from 0.87 to 1.0. CONCLUSION: The very high level of agreement between institutional patient records and the PTAC data for fields compared in this study supports the validity of the PTAC database. For the first time, a population-based patient transfer database has been established. Although it was created during an emergency situation and data collection is dependent on front-line medical workers, the PTAC data has achieved a high level of validity, perhaps even higher than many purpose built databases created during non-emergency settings.

Database Management Systems↗

PubMed2000

Pregnancy rates after embryo transfer depend on the provider at embryo transfer.

OBJECTIVE: To evaluate the effect of individual providers on pregnancy outcome after embryo transfer. DESIGN: Retrospective data analysis. SETTING: University-based tertiary-care assisted reproductive technology program with 10 physician-providers. PATIENT(S): Six hundred and seventeen women who underwent 854 fresh embryo transfers between January 1996 and January 1999. INTERVENTION(S): Pregnancies after embryo transfer were recorded for each provider. MAIN OUTCOME MEASURE(S): Establishment of a clinical pregnancy. RESULT(S): Three hundred ninety-three clinical pregnancies resulted from 854 embryo transfers, for an overall clinical pregnancy rate of 46.0% per embryo transfer. Three hundred forty-seven (40.6%) pregnancies were ongoing. The clinical pregnancy rate varied significantly between providers: for example, 17.0% (47 transfers) vs. 54.3% (57 transfers) (P<.05). Similarly, the ratio of high-grade embryos required to produce a gestational sac differed between providers. The number or quality of embryos transferred did not differ significantly. CONCLUSION(S): Significant differences were observed in pregnancy rates after embryo transfer done by different providers, suggesting that embryo transfer technique may influence pregnancy outcome in assisted reproductive technology.

Adult↗

PubMed2001

Sex ratio and birth weights of infants born as a result of blastocyst transfers compared with early cleavage stage embryo transfers.

OBJECTIVE: To analyze the birth weights and sex ratio of infants born as a result of blastocyst transfer and compare them with data resulting from the transfer of early-cleavage stage embryos. DESIGN: Retrospective analysis. SETTING: Monash IVF (private in vitro fertilization clinic). PATIENTS(S): One hundred twenty-five infertile patients who became pregnant after IVF procedures involving blastocyst transfer. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Sex ratio and birth weights of infants born after blastocyst transfer. RESULT(S): The sex ratio of 129.6 for infants born after blastocyst transfer was not significantly different from the sex ratio calculated from data compiled by NPSU for births resulting from early cleavage stage embryo transfers at Monash IVF (100.6) and all other assisted conception units in Australia and New Zealand (97.9). No differences were observed in the combined mean birth weight of male and female infants born as a result of blastocyst transfers and early-cleavage stage embryo transfers. CONCLUSION(S): There is no evidence of abnormal fetal growth or a shift in the sex ratio for infants born as a result of blastocyst transfer when compared with the case of births resulting from early cleavage stage embryo transfers within our unit or all other assisted conception units in Australia and New Zealand.

Birth Weight↗

PubMed2003

Embryo transfer: hysteroscopic assessment of transfer catheter effects on the endometrium.

So far as is known, this is the first series to report the effects of embryo transfers on endometrial integrity as assessed by direct hysteroscopic visualization. Subjects (n = 30) were patients of reproductive age undergoing diagnostic hysteroscopy. A mock embryo transfer was performed by a single clinician, immediately followed by saline hysteroscopy using a 2.7 mm hysteroscope. Hegar dilators or uterine sounds were not used. Representative video clips were recorded for independent assessment of endometrial integrity. (The movie sequence may be purchased for viewing on the internet at www.rbmonline.com/Article/1040; it is free to web subscribers.) Outcomes measured were ease of transfer (easy, moderate, difficult, very difficult) and details of the transfer technique. Endometrial damage was independently assessed and graded as follows: none, minor, moderate or severe. Of the easy transfers, 54% showed no endometrial damage. However, there 37% showed moderate to severe damage in the easy transfer group. Of the moderately difficult transfers, there was no clear association between perceived difficulty of transfer and amount of endometrial damage. Clinical perception of ease of transfer does not correlate well with the degree of endometrial disruption (P = 0.41). Use of hysteroscopy offers a unique insight into the effects of embryo transfer on endometrial integrity.

Adult↗

PubMed1995

Kinetics and inhibition of lipid exchange catalyzed by plasma cholesteryl ester transfer protein (lipid transfer protein).

The cholesteryl ester transfer protein-catalyzed cholesteryl ester transfer is inhibited by two compounds identified by a large-scale screening of cholesterol backbone-containing molecules. Kinetic analysis shows that U-95,594, an amino steroid, inhibits competitively the cholesteryl ester transfer protein-catalyzed transfer of both cholesteryl esters and triglycerides, as well from high-density lipoproteins as from synthetic microemulsions. In contrast, U-617, an organomercurial derivative of cholesterol, inhibits competitively the transfer of cholesteryl ester from either donor but is without any effect on triglyceride transfer. In addition to the rapid, competitive inhibition of cholesteryl ester transfer, U-617 also slowly and reversibly reacts with cholesteryl ester transfer protein to produce an additional 10-fold decrease in cholesteryl ester transfer activity but, again, without effect on triglyceride transfer.

Animals↗

PubMed1996

Neutralization and transfer of lipopolysaccharide by phospholipid transfer protein.

Phospholipid transfer protein (PLTP) and lipopolysaccharide-binding protein (LPB) are lipid transfer proteins found in human plasma. PLTP shares 24% sequence similarity with LBP. PLTP mediates the transfer and exchange of phospholipids between lipoprotein particles, whereas LBP transfers bacterial lipopolysaccharide (LPS) either to lipoprotein particles or to CD14, a soluble and cell-surface receptor for LPS. We asked whether PLTP could interact with LPS and mediate the transfer of LPS to lipoproteins or to CD14. PLTP was able to bind and neutralize LPS: incubation of LPS with purified recombinant PLTP (rPLTP) resulted in the inhibition of the ability of LPS to stimulate adhesive responses of neutrophils, and addition of rPLTP to blood inhibited cytokine production in response to LPS. Transfer of LPS by rPLTP was examined using fluorescence dequenching experiments and native gel electrophoresis. The results suggested that rPLTP was able to mediate the exchange of LPS between micelles and the transfer of LPS to reconstituted HDL particles, but it did not transfer LPS to CD14. Consonant with these findings, rPLTP did not mediate CD14-dependent adhesive responses of neutrophils to LPS. These results suggest that while PLTP and LBP both bind and transfer LPS, PLTP is unable to transfer LPS to CD14 and thus does not mediate responses of cells to LPS.

Boron Compounds↗

PubMed2000

Experience with the elective transfer of two embryos under the conditions of the german embryo protection law: results of a retrospective data analysis of 2573 transfer cycles.

The German embryo protection law (Embryonenschutzgesetz, ESchG) does not allow embryo selection. Therefore, only as many oocytes at the pronuclear stage (PN), as are planned to be transferred, are allowed to be cultured. It is not known whether, under these conditions, it is possible to reduce the number of embryos for transfer without a corresponding reduction of the overall pregnancy rate (PR). We retrospectively analysed 2573 consecutive transfer cycles following either in-vitro fertilization (IVF) or IVF/intracytoplasmic sperm injection. Out of these cycles, 234, 329 and 792 were performed with one, two, and three embryos respectively, because only that number was available (non-elective transfer). Another 123 and 1095 transfer cycles were performed with two and three embryos, respectively, which were selected from a higher number of PN oocytes (elective transfer). The clinical ongoing PR were 3.9, 9.1 and 17.7% respectively for the groups with non-elective transfer of 1, 2 and 3 embryos, and 22.0 and 22.5% for the groups with elective transfers with two and three embryos, respectively. There was no statistically significant difference in PR between the two elective embryo transfer groups up to the age of 40 years. The multiple pregnancy rate was reduced by 7.9%. The reduction of the number of embryos transferred from three to two can be performed even under the conditions of the ESchG without an effect on the overall PR.

Abortion, Spontaneous↗

PubMed2004

Blastocyst versus early cleavage embryo transfer: a retrospective analysis of 4,165 transfers.

PURPOSE: To compare the clinical outcomes after the transfer of blastocysts versus early cleavage embryos in assisted reproduction technologies (ART). METHODS: A retrospective analysis of all the ovarian stimulation-in vitro fertilization-embryo transfer cycles performed at the Centre for Human Reproduction, Athens, Greece, between June 1997 and December 2001. RESULTS: The number of blastocysts transferred per ET was significantly lower compared to that of all early cleavage embryos. The implantation rate of blastocysts was significantly higher compared to that of all other modes of transfer. Clinical pregnancy rate after the transfer of blastocysts was significantly increased compared to that after transfer of any early cleavage embryo. The viable pregnancy rate after the transfer of blastocysts was significantly increased only compared to that after the transfer of day-2 embryos. There were no significant differences regarding the multiple gestation rates among the various modes of transfer. CONCLUSION: The use of blastocysts in ART is beneficial when compared to that of day-2 embryos and at least comparable to that of day-3 embryos. Blastocyst culture and transfer remains a favourable and promising option in ART.

Adult↗

PubMed1995

High-order oocyte transfer in gamete intrafallopian transfer patients 40 or more years of age.

OBJECTIVE: To analyze whether a policy of high-order oocyte transfer would be effective in women > or = 40 years of age who are undergoing GIFT, and further, whether a specific subgroup of these patients could be identified where clinical pregnancy was more likely to occur. DESIGN: Prospective descriptive study. SETTING: Patients in a university-based reproductive endocrinology and infertility practice. PATIENTS: Infertile women > or = 40 years of age who underwent GIFT cycles between January, 1990 and December, 1993 after not having achieved pregnancy with at least three previous cycles of superovulation and intrauterine insemination. INTERVENTIONS: Gamete intrafallopian transfer was performed after controlled ovarian hyperstimulation with hMGs. High-order oocyte transfer was employed. MAIN OUTCOME MEASURES: Clinical pregnancy rates (PRs). RESULTS: The overall clinical PR was 24.5% per retrieval (12/49) and 25.5% per transfer (12/47). A significantly higher number of oocytes were retrieved in patients who became pregnant than those who did not. Patient age, cycle day 3 FSH level, E2 level on the day of hCG administration, number of oocytes transferred, and total number of motile sperm transferred did not differ significantly between the two groups. The clinical PR per transfer was significantly higher in patients with more than five oocytes transferred (10/27, 37%) versus those with five or less oocytes transferred (2/20, 10%). No multiple gestations were obtained. CONCLUSION: The number of oocytes retrieved in women > or = 40 years of age undergoing GIFT is the main determinant predicting clinical pregnancy. High-order oocyte transfer seems to lead to a favorable PR while the risk of multiple gestation is limited.

Adult↗

PubMed1998

The C-terminus of phosphatidylinositol transfer protein modulates membrane interactions and transfer activity but not phospholipid binding.

Rat phosphatidylinositol transfer protein (PITP) is a 32 kDa protein containing 271 amino acids. It is involved in a number of cell functions including secretion and cell signaling. To further characterize structure/activity relationships of PITP, two C-terminal truncated derivatives, PITP(1-259) and PITP(1-253), were produced in Escherichia coli and purified to homogeneity. PITP(1-259) had transfer activity equal to 30-40% to that of native PITP in transfer of either phosphatidylcholine (PC) or phosphatidylinositol (PI) when transfer was measured using 95/5 mol% PC/PI donor and acceptor vesicles; PITP(1-253) had only slight transfer activity, even under the most favorable assay conditions. Thus, amino acids 254-258 are critical for transfer activity. The transfer activity of PITP(1-259) was strongly dependent on the composition of the donor and acceptor vesicles. With 100 mol% PC donor and acceptor vesicles, PITP(1-259) transfer activity ranged from 70 to 100% to that of PITP. The presence of 2 mol% phosphatidic acid (PA) in either donor or acceptor vesicles reduced transfer activity to between 10 and 20% that of full-length PITP under the same conditions. If both donor and acceptor contained 2% PA, PITP(1-259) was essentially inactive, though the activity of PITP was not affected significantly under these conditions. PITP(1-253) and PITP(1-259) bind much more avidly to vesicles than does PITP, and this enhanced binding reflects increased electrostatic interactions. Thus, the C-terminal residues modulate the affinity of PITP for vesicles and the efficiency of phospholipid transfer.

Animals↗

PubMed1992

Transneuronal transfer of herpes simplex virus type 1 (HSV 1) from mixed limb nerves to the CNS. I. Sequence of transfer from sensory, motor, and sympathetic nerve fibres to the spinal cord.

The time course of transneuronal transfer of Herpes simplex virus type 1 (HSV 1) from sensory, motor, and sympathetic nerve fibres to connected spinal neurones was examined. After injection of a constant number of infectious units into distal forelimb or hindlimb nerves of inbred rats of the same age, the extent of viral transfer was strictly dependent on the survival time postinoculation (p.i.). Retrograde transport to somatic motoneurones occurred at 28-29 hours p.i. (stage 1), in synchrony with anterograde transneuronal transfer via small cutaneous afferents (to laminae I-II). At 36-43 hours p.i. (stage 2), retrograde transneuronal transfer from sympathetic nerve fibres first labelled sympathetic preganglionic neurones. At 48-51 hours p.i. (stage 3), transfer via sensory and sympathetic axons became more extensive, labelling laminae III-IV and other preganglionic neurones. Transneuronal transfer from large muscle afferents and motoneurones (to Clarke's columns and the spinal intermediate zone) occurred only at 66-78 hours p.i. (stage 4). Further increases in distribution (stages 5-6) obtained between 78 and 97 hours p.i. may reflect both specific labelling of second and third order neurones and a gradual local loss of specificity. These results indicate that transfer of HSV 1 occurs through all main classes of peripheral axons, but that both anterograde and retrograde transneuronal transfer from small (unmyelinated and fine myelinated) cutaneous and sympathetic axons precedes transfer from large (myelinated) cutaneous and muscle afferents and motor axons. Analysis of viral transfer at sequential intervals is required to distinguish serially connected neurones, determine the route of labelling, and ensure its specificity.

Animals↗

PubMed1991

Lipid transfer particle-catalyzed transfer of lipoprotein-associated diacylglycerol and long chain aliphatic hydrocarbons.

Following injection of [1-14C]acetate into the sphinx moth, Manduca sexta, radiolabel was incorporated into lipid components of the major hemolymph lipoprotein, adult high density lipophorin (HDLp-A). Analysis of the labeled lipids by thin layer chromatography and radiochromatogram scanning revealed incorporation of radioactivity into the diacylglycerol (DAG) and hydrocarbon components as well as a third lipid fraction of unknown identity. Lipid transfer experiments were carried out using 14C-lipid HDLp-A and human low density lipoprotein (LDL) as donor/acceptor substrates and M. sexta lipid transfer particle (LTP) as catalyst. In control incubations lacking LTP, nearly all of the radiolabeled lipid remained associated with HDLp-A. LTP, however, induced a time-dependent vectorial transfer of radiolabeled lipid from HDLp-A to LDL. Lipid analysis of the LDL fraction, reisolated following the transfer reaction, revealed that labeled lipid components originally associated with HDLp-A were present in the acceptor LDL particles. The recovery of radiolabeled hydrocarbon associated with LDL demonstrates the capacity of LTP to facilitate transfer of these long chain, extremely hydrophobic, lipids and suggests LTP may function as a mediator of hydrocarbon transport and metabolism in vivo. When acceptor LDL particles were analyzed prior to complete transfer of HDLp-A-associated lipid it was observed that DAG was transferred preferentially during the initial stages of the reaction after which hydrocarbon transfer increased. This result suggests that LTP may have a lipid substrate preference for DAG versus hydrocarbon. Alternatively the observed preference for DAG may be a function of the relative accessibility of the substrates within the donor lipoprotein. In other experiments it was demonstrated that, unlike other lipids associated with HDLp-A, free fatty acid spontaneously transfers to LDL in the absence of lipid transfer catalyst.

Acetates↗

PubMed1998

A comparison of laboratory data in perinatal transfers at Baystate Medical Center and transferring hospitals.

Objective: Perinatal transfers come to Baystate Medical Center (BMC), a tertiary hospital with level III nursery, for treatment of pregnancy-related complications such as preterm labor, PPROM, PIH, diabetes, and bleeding problems. We postulated that Baystate Medical Center, a teaching hospital, must repeat most of the laboratory tests ordered by the community hospitals transferring these pregnant patients.Methods: A comparison of laboratory tests ordered by the transferring hospital and Baystate Medical Center was done in a retrospective chart review. Among the 92 charts reviewed, 42 perinatal transfer patients with PTL and PPROM, excluding patients with diabetes, PIH, and other complications, were included in the study.Results: A significant difference (P <.001 by Student t test) was found between the number of laboratory tests ordered by Baystate Medical Center and the outside hospital. Ten laboratory tests, such as white count, hematocrit, differential, cervical cultures, urinalysis and culture, tox screen, type and screen, and ultrasounds, were ordered by BMC in comparison to only three laboratory tests ordered by the transferring doctors. In comparing patients directly admitted to Baystate for PTL or PPROM with the perinatal transfer patients, there was no significant difference between the number of laboratory tests ordered. However, perinatal transfers had a greater percentage of PPROM and delivery prior to 36 weeks.Conclusion: In conclusion, there is limited redundancy in laboratory testing in perinatal transfer patients when they are transferred from one institution to the another. Diagnosis of PTL is difficult and a panel of laboratory tests have become standards in finding causes at BMC. Allowing the tertiary hospital to work up the perinatal transfer patients is an efficient way of allocating health care.

Journal Article↗

PubMed1994

Pathway of proton transfer in bacterial reaction centers: role of aspartate-L213 in proton transfers associated with reduction of quinoneto dihydroquinone.

The role of Asp-L213 in proton transfer to reduced quinone QB in the reaction center (RC) from Rhodobacter sphaeroides was studied by site-directed replacement of Asp with residues having different proton donor properties. Reaction centers (RCs) with Asn, Leu, Thr, and Ser at L213 had greatly reduced (approximately 6000-fold) proton-coupled electron transfer [kAB(2)] and proton uptake rates associated with the second electron reduction of QB (QA- QB- + 2H(+)-->QAQBH2) compared to native RCs. RCs containing Glu at L213 showed faster (approximately 90-fold) electron and proton transfer rates than the other mutant RCs but were still reduced (approximately 70-fold) compared with native RCs. These results show that kAB(2) is larger when a carboxylic acid occupies the L213 site, consistent with the proposal that Asp-L213 is a component of a proton transfer chain. The reduced kAB(2) observed with Glu versus Asp at L213 suggests that Asp at L213 is important for proton transfer for some other reason in addition to its proton transfer capabilities. Glu-L213 is estimated to have a higher apparent pKa (pKa > or = 7) than Asp-L213 (pKa < or = 4), as indicated by the slower rate of charge recombination (D+QAQB(-)-->DQAQB) in the mutant RCs. The importance of the pKa and charge of the residue at L213 for proton transfer are discussed. Based on these studies, a model for proton transfer is proposed in which Asp-L213 contributes to proton transfer in native RCs in two ways: (1) it is a component of a proton transfer chain connecting the buried QB molecule with the solvent and/or (2) it provides a negative charge that stabilizes a proton on or near QB.

Aspartic Acid↗

PubMed1994

Selective transfer of cholesteryl ester over triglyceride by human plasma lipid transfer protein between apolipoprotein-activated lipid microemulsions.

The substrate-specific rate of the human plasma lipid transfer protein (LTP) reaction was studied using pyrene-labeled substrate lipid analogues as probes for various lipids, by monitoring the ratio of the fluorescence intensities of their excimers to those of their monomers as an indicator of pyrene concentration in the microenvironment. Transfer of cholesteryl ester (CE) and triglyceride (TG) was demonstrated between human high-density lipoproteins, between low-density lipoproteins, and between these two lipoprotein, and the specific fractional transfer rate of CE was always higher than that of TG by a factor of 2.4-7.9. On the other hand, the transfer by LTP of CE, TG, and phosphatidylcholine (PC) was also demonstrated between lipid microemulsions having an average diameter of 25-26 nm using the same probes, but only when the emulsions were activated by apolipoproteins A-I, A-II, E, or C-III. The maximally activated rates of the transfer of CE and TG were the same when measured between the emulsions with cores composed exclusively of either lipid. The specific fractional transfer rate of pyrene-CE, however, was inversely proportional to the percentage of CE in the TG core of the emulsions, and the initial transfer of TG was almost completely inhibited by the presence of small percentages of CE in the TG core. Thus, the transfer of CE between the emulsions is highly selective over that of TG by orders of magnitude, much more selective than the reaction between any natural plasma lipoproteins, but this selectivity is not a rate-limiting step of the overall LTP reaction. The maximally activated LTP-catalyzed transfer rate of PC between the emulsions was somewhat higher than that of CE or TG and was not affected by the composition of the core lipids of the emulsion, TG or CE. When an excess amount of LTP was incubated with emulsion containing a small percentage of pyrene-CE in the TG core in the absence of the acceptor particles, excimer fluorescence rapidly decreased to the base line, and this change was suppressed when pyrene-CE was diluted with CE in the core. This result may indicate that LTP selectively disrupts pyrene-CE excimer formation on the basis of its selective interaction with the CE molecule over TG in the emulsion system as a putative background mechanism for the selective transfer of CE.

Apolipoprotein A-I↗

PubMed2004

Experimental and theoretical studies of charge transfer and deuterium ion transfer between D2O+ and C2H4.

The charge transfer and deuterium ion transfer reactions between D(2)O(+) and C(2)H(4) have been studied using the crossed beam technique at relative collision energies below one electron volt and by density functional theory (DFT) calculations. Both direct and rearrangement charge transfer processes are observed, forming C(2)H(4) (+) and C(2)H(3)D(+), respectively. Independent of collision energy, deuterium ion transfer accounts for approximately 20% of the reactive collisions. Between 22 and 36 % of charge transfer collisions occur with rearrangement. In both charge transfer processes, comparison of the internal energy distributions of products with the photoelectron spectrum of C(2)H(4) shows that Franck-Condon factors determine energy disposal in these channels. DFT calculations provide evidence for transient intermediates that undergo H/D migration with rearrangement, but with minimal modification of the product energy distributions determined by long range electron transfer. The cross section for charge transfer with rearrangement is approximately 10(3) larger than predicted from the Rice-Ramsperger-Kassel-Marcus isomerization rate in transient complexes, suggesting a nonstatistical mechanism for H/D exchange. DFT calculations suggest that reactive trajectories for deuterium ion transfer follow a pathway in which a deuterium atom from D(2)O(+) approaches the pi-cloud of ethylene along the perpendicular bisector of the C-C bond. The product kinetic energy distributions exhibit structure consistent with vibrational motion of the D-atom in the bridged C(2)H(4)D(+) product perpendicular to the C-C bond. The reaction quantitatively transforms the reaction exothermicity into internal excitation of the products, consistent with mixed energy release in which the deuterium ion is transferred in a configuration in which both the breaking and the forming bonds are extended.

Journal Article↗

PubMed1990

Pathway of proton transfer in bacterial reaction centers: replacement of serine-L223 by alanine inhibits electron and proton transfers associated with reduction of quinone to dihydroquinone.

The pathway of proton transfer in the reaction center (RC) from Rhodobacter sphaeroides was investigated by site-directed mutagenesis. Ser-L223, a putative proton donor that forms a hydrogen bond with the secondary quinone acceptor QB, was replaced with Ala and Thr. RCs with Ala-L223 displayed reduced electron transfer and proton uptake rates in the reaction QA-QB- + 2H+----QAQBH2. The rate constant for this reaction, k(2)AB, was found to be reduced approximately 350-fold to 4.0 +/- 0.2 s-1. Proton uptake measurements using a pH indicator dye showed a rapid uptake of 1 H+ per RC followed by a slower uptake of 1 H+ per RC at a rate of 4.1 +/- 0.1 s-1; native RCs showed a rapid uptake of 2H+ per RC. Evidence is provided that these changes were not due to gross structural changes in the binding site of QB. RCs with Thr-L223 showed little reduction in the rates of electron and proton transfer. These results indicate that proton transfer from the hydroxyl group of Ser-L223 or Thr-L223 is required for fast electron and proton transfer associated with the formation of the dihydroquinone QH2. In contrast, previous work showed that replacing Glu-L212, another putative proton donor to QB, with Gln slowed proton uptake from solution without significantly altering electron transfer. We propose a model that involves two distinct proton transfer steps. The first step occurs prior to transfer of the second electron to QB and involves proton transfer from Ser-L223. The second step occurs after this electron transfer through a pathway involving Glu-L212.

Alanine↗