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Biomedical subjects

C Preston

Publications and source records attributed to C Preston.

At least 37 records · Page 2Linked to original sources
PubMed1991

Protease treatments of photosystem II membrane fragments reveal that there are four separate high-affinity Mn-binding sites.

The "high-affinity Mn-binding site" in Mn-depleted photosystem II (PS II) membrane fragments isolated from Scenedesmus obliquus was examined by using the diphenylcarbazide (DPC)/Mn2+ non-competitive inhibition assay [Preston, C., & Seibert, M. (1991) Biochemistry (preceding paper in this issue)]. Different proteases were used to degrade lumenal surface protein segments from these PS II membranes, and a total of four independent high-affinity Mn-binding sites (ligands) were identified. Carboxypeptidase A, subtilisin, and Staphylococcus aureus V8 protease each degrade one of two high-affinity Mn-binding sites sensitive to the histidine chemical modifier diethyl pyrocarbonate (DEPC). However, sequential treatment experiments indicate that subtilisin degrades a DEPC-sensitive Mn-binding site that is different from the one degraded by the other two proteases. Trypsin also was found to degrade one of the DEPC-sensitive Mn-binding sites (that degraded by carboxypeptidase A and V8 protease). In addition, trypsin degrades one of two 1-ethyl-3-[(3-dimethylamino)propyl]carbodiimide (EDC) sensitive Mn-binding sites, but only in the absence of the 30-kDa extrinsic protein. Thus, the 30-kDa extrinsic protein associated with O2 evolution appears to protect the EDC-sensitive binding site from trypsin degradation. No protease has yet been identified that will degrade the trypsin-insensitive EDC-sensitive Mn-binding site. Under the conditions of the assay (high DPC concentration), more than three Mn per reaction center were found bound to the membrane with a KM of about 0.4 microM, as determined by direct metal analysis. This is consistent with the idea that each of the four high-affinity sites binds (or provides a ligand for) one of four Mn.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites↗
PubMed1991

Intraplacental sonolucent spaces: incidences and relevance to chorionic villus sampling.

Detailed ultrasound examination of the placentae from 293 consecutive women requesting first-trimester chorionic villus sampling (CVS) showed evidence of intraplacental sonolucent spaces with varying density in 42.3 per cent of these placentae. Their presence, however, did not complicate the subsequent course of these women's pregnancies. Their prime significance relates to CVS, where inadvertent entry into these areas can lead to bleeding and contamination of the villus specimens with blood. A search for these spaces should be made before sampling, and when present, they should be avoided wherever possible.

Chorionic Villi Sampling↗
PubMed1991

Resistance to the herbicide paraquat and increased tolerance to photoinhibition are not correlated in several weed species.

Photoinhibition was examined in paraquat-resistant and paraquat-susceptible biotypes of Hordeum glaucum Steud., Hordeum leporinum Link., Arctotheca calendula (L.) Levyns., and Conyza bonariensis (L.) Cronq. Plants were photoinhibited at low temperature, and the extent of photoinhibition determined by O(2) evolution and 77 K fluorescence. No difference in the degree of photoinhibition was detected between paraquat-resistant and paraquat-susceptible biotypes for any of the species examined. C. bonariensis plants were also photoinhibited by treatment without CO(2) at either 21% (volume/volume) O(2) or 4% (volume/volume) O(2), and again no difference was observed between the paraquat-resistant and paraquat-susceptible biotypes in reduction of the ratio of variable fluorescence to maximal fluorescence. This is in contrast to a recent report (MAK Jansen, Y Shaaltiel, D Kazzes, O Canaani, S Malkin, J Gressel, [1989] Plant Physiol 91: 1174-1178 in which it was claimed that a paraquat-resistant biotype of C. bonariensis was more tolerant of photoinhibition than a paraquat-susceptible biotype. We conclude that paraquat-resistant biotypes of these plant species are not more tolerant of photoinhibition when compared with the paraquat-susceptible biotypes.

Journal Article↗
PubMed1990

Chlorophyll a fluorescence lifetime distributions in open and closed photosystem II reaction center preparations.

We have measured the decay of chlorophyll a fluorescence at 4 degrees C under anaerobic conditions in stabilized photosystem II reaction center complex isolated from spinach, using multifrequency (2-400 MHz) cross-correlation phase fluorometry. Examination of our data shows that although the fluorescence decay of open reaction centers (i.e., when both the electron donor P-680 and the electron acceptor pheophytin are capable of engaging in charge separation) can be analyzed as a multiexponential decay, another representation of the data is obtained when the decay is analyzed using a continuous distribution of lifetimes. Our results on the open reaction center differ from the two lifetime components of 25 ps and 35 ns published by Mimuro et al. (Biochim. Biophys. Acta 933 (1988) 478-486) for the D1-D2-cytochrome b-559 complex, obtained for F682 at 4 degrees C by a time-resolved photon-counting spectrofluorometer. When the reaction centers are closed by pretreatment with sodium dithionite and methyl viologen followed by exposure to laser excitation, conditions known to result in accumulation of reduced pheophytin, a dramatic decrease in the contribution of the slow lifetime component(s) is observed. These results suggest that the slow distribution lifetime component(s) in the 5-20 ns range originate(s) in the back reaction of the charge separated state. On the other hand, the fast lifetime component(s) in the picosecond range may be only partially related to the charge separation, since no dramatic change is observed upon closure of the reaction center. Perhaps, this component is related, in part, to the excitation energy migration among the various chromophores in the reaction center preparations.

Chlorophyll↗
PubMed1989

The behavioural effects of MK-801: a comparison with antagonists acting non-competitively and competitively at the NMDA receptor.

The selective non-competitive NMDA receptor antagonist, MK-801, potently blocked convulsions induced in the mouse by N-methyl-DL-aspartic acid (NMDLA) with an i.v. ED50 dose of 0.2 mg/kg. Similar doses of MK-801 were also effective in blocking seizures induced by pentylenetetrazol (PTZ), electroshock and by sound in audiogenic seizure-prone animals. Other less selective non-competitive NMDA receptor antagonists including phencyclidine (PCP), thienylcyclohexylpiperidine (TCP), (+)-N-allylnormetazocine [+)-NANM, (+)-SKF 10,047) and ketamine also blocked NMDLA-induced seizures with a rank order of potency of MK-801 greater than PCP greater than TCP = (+)-NANM greater than ketamine. The competitive NMDA receptor antagonist, 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) blocked NMDLA-induced seizures with an ED50 of 4.5 mg/kg, 22- and 560-fold more potently than the competitive antagonists, 2-DL-amino-7-phosphonoheptanoic acid (2-APH) and 2-DL-amino-5-phosphonovaleric acid (2-APV), respectively. MK-801 was the most potent of the non-competitive antagonists to induce a motor syndrome including head weaving, body rolling, increased locomotion and ataxia, characteristic of the behavioural response to PCP in the mouse. The syndrome was also present following injection of the competitive NMDA receptor antagonists, although they were generally less potent (probably a reflection of poor brain penetration) and less efficacious than the non-competitive antagonists. For all compounds except CPP, the anticonvulsant ED50 dose was close to the minimum effective dose to induce motor stimulation: CPP was 5- to 10-fold more potent as an anticonvulsant.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Bleeding as a consequence of chorion villus sampling.

A series of 4 separate studies were conducted to assess the incidence and short term consequence of bleeding associated with chorion villus sampling. Results support previous reports that risk of foetal-maternal transfusion as suggested by a rise in maternal serum alpha-fetoprotein (MSAFP) can occur. This occurrence is not consistent and need not be obvious even after therapeutic abortion. It is also transient and did not complicate mid-trimester neural tube screening or subsequent course of pregnancy. Eighty-seven percent of blood contaminating villus samples are of maternal origin. Following diagnosis 37% of patients reported some vaginal bleeding. This is mainly in the form of spotting which did not preclude normal pregnancy. Foetal loss occurred in 4 of the patients when bleeding considered heavier than spotting continued. In rhesus negative patients prophylactic anti-D gamma-globulin is advised, since neither Kleihauer counts nor MSAFP estimation reliably detect all foetal-maternal transfusions.

Chorionic Villi Sampling↗
PubMed1989

Mourning and reminiscence: parallel psychotherapeutic processes for elderly people.

Mourning and reminiscence are therapeutic processes common in therapeutic work with the elderly. However, a theoretical explanation of why they are effective has been lacking. Personal construct theory accounts for both in terms of the search of elderly persons for validation of their construct systems. In this article, this explanation of the parallel psychotherapeutic processes is explored, together with relevant information from the literature on mourning and reminiscence. Therapeutic case studies illustrate the characteristics of the two processes and the relationship between them.

Aged↗
PubMed1987

A prospective study of spontaneous miscarriage in ultrasonically normal pregnancies and relevance to chorion villus sampling.

A total of 1,068 patients were examined by ultrasound to ensure normality of pregnancy and followed prospectively from booking until 28 weeks. The spontaneous miscarriage rate was 2.7 per cent occurring within the first 16 weeks. Threatened miscarriage was associated with a 38 per cent fetal loss. Miscarriage was less likely as pregnancy advanced. The reduction in subsequent miscarriage rate before 11 weeks and from 11 weeks onwards is statistically significant (p less than 0.001). Gravidity, maternal age and a history of previous fetal loss did not contribute significantly to the miscarriage rate. Patients with a history of fetal loss were more likely to experience a threatened miscarriage. The relevance of these findings to chorion villus sampling is discussed.

Abortion, Spontaneous↗
PubMed1986

Proton nuclear magnetic resonance studies of soybean lectin-monosaccharide interactions: computer analysis of complex binding behavior.

1H NMR was used to quantify soybean lectin binding to monosaccharides, using presaturation of HOD plus a spin-echo sequence to observe sugar -NHCOCH3 and -OCH3 to below 0.01 mM. Binding is in the very-slow-exchange limit; there is no broadening or shifting and only unbound sugar is observed for pH 5 to 8 and 25 to 75 degrees C. Preliminary results were consistent with those previously reported for methyl 2-acetamido-2-deoxy-alpha-D-galactopyranoside (Me alpha-D-GalNAcp) (K = 3 X 10(4) liters mol-1 with four sites per tetramer). More detailed studies, however, gave concave Scatchard plots for methyl 2-acetamido-2-deoxy-alpha- and beta-D-galactopyranoside, (Me alpha- and Me beta-D-GalNAcp), best fitted using K1 values of (6-12) X 10(4) liters mol-1, K2 values less than or equal to 0.5 X 10(4) liters mol-1, and four sites of each type in D2O or 80% H2O at 25 degrees C and pH 7.2. Data for methyl alpha-D-galactopyranoside were fitted with K = 0.5 X 10(4) liters mol-1 and eight sites of the same K. Monosaccharides may be binding in the recently reported "hydrophobic sites" of soybean lectin. Both methyl 2-acetamido-2-deoxy-beta-D-galactofuranoside (Me beta-D-GalNAcf) and methyl 2-acetamido-2-deoxy-alpha-D-glucopyranoside (Me alpha-D-GlcNAcP) showed some binding by 1H NMR; K's were similar to those for the high-affinity sugars, but the occupancy was much lower. The soybean lectin in this study was saturated in Ca2+ (greater than or equal to 4 mol/tetramer), but low in Mn2+, with Mn2+ plus Mg2+ less than 4. We report new melting points for D-N-acetylgalactosamine, Me alpha-D-GlcNAcp, Me beta-D-GalNAcp, and Me beta-D-GalNAcf, and a fully listed program for fitting curved Scatchard plots using Apple IIc and IIe computers.

Computers↗
PubMed1985

Sources of anxiety in drug addiction.

A sample of drug addicts (N = 60) in treatment were interviewed, and their descriptions of their lives were elicited and recorded. Their scores on a measure of anxiety based on content analysis of these descriptions were compared with those of two other groups of people matched for sex and age. The chief element in the pattern of anxiety that differentiated the groups was shame. Addicts also expressed more guilt, loneliness, fear of death, and vague worries than the other groups. This pattern was found to vary with the criminal history of the addicts and their counselors' assessment of them. Implications were discussed.

Adolescent↗
PubMed1985

Prediction of response to radiotherapy for localised prostatic cancer.

Fifty-one patients with TO-4 NX MO carcinoma of the prostate were treated by external beam radiotherapy. Comparison with 40 patients with TO-3 NX MO disease, whose treatment was deferred initially, showed a higher incidence of local progression in the untreated patients. Age at presentation and initial T category did not have a significant influence upon the probability of disease progression after radiotherapy, whereas all but one of the irradiated patients with Gleason sum scores greater than or equal to 6 progressed. Treatment-related morbidity was appreciable and prolonged proctitis occurred in 31 patients. There was one treatment-related death. Biopsy 1 year after treatment did not yield information of prognostic significance. It is recommended that the selection of patients with localised carcinoma of the prostate for treatment by radiotherapy is based on histological grade. The Gleason score is a practical method for identifying those who would best be treated by other methods.

Aged↗
PubMed1985

The addiction experience as a function of the addict's history.

Application of personal construct theory to addicts in treatment led to a series of hypotheses about their psychological reactions and how these might differ with differences in their histories. Their scores on a set of content analysis scales were compared with those of a relatively non-stressed group and a relatively stressed group matched for sex and age. The chief element in the pattern of experiential elements which was identified was uncertainty. Addicts also expressed more anxiety, depression and anger (directly and indirectly) and reported fewer social interactions than the non-stressed group; however, for most of these elements they were similar to the similarly stressed group of young people with whom they were compared. The pattern of experience of addiction was found to vary according to the employment, addiction and criminal histories of the addicts, their treatment histories as represented by their counsellors' assessments of them and the social supports available to them.

Adolescent↗
PubMed1982

Occupational stress, Type A behavior, and physical well being.

In the context of a person-environment fit framework, organizational level and the Type A behavior pattern of managers were found to moderate the stressor, satisfaction, and physiology associations. For nurses, Type A behavior pattern was a much more significant moderator of the person-environment fit than were the nurses' specialty work activities.

Administrative Personnel↗
PubMed1980

Biochemical and clinical responses to dichloromethylene diphosphonate (Cl2MDP) in Paget's disease of bone.

Dichloromethylene diphosphonate (Cl2MDP, or clodronate disodium) is one of the most potent of the known diphosphonates as an inhibitor of bone resorption and differs from EHDP in that it does not inhibit skeletal mineralization. It is one of the second generation diphosphonates now undergoing clinical evaluation. In the study described here Cl2MDP was given by mouth (800-1600 mg/day for 6 months) to 35 patients with symptomatic Paget's disease of bone. Cl2MDP induced a marked fall in serum alkaline phosphatase and urinary hydroxyproline to normal or near normal values in all patients. This was accompanied by clinical improvement in all but 4 patients. Cl2MDP appears to be another effective oral drug for the treatment of Paget's disease of bone and compares favorably with the calcitonins and EHDP.

Alkaline Phosphatase↗
PubMed1978

Regulation of the tubular transport of phosphate in the rat: role of parathyroid hormone and 1,25-dihydroxyvitamin D3.

The reduced capability of the tubular Pi transport to adapt to a high Pi diet in TPTX rats can be normalized by physiological doses of 1,25-(OH)2D3. This suggests that the chronic consequence of a lack of PTH could be due, at least in part, to the reduced production of 1,25-(OH)2D3. The mechanism of Pi adaptation appears to be the most important regulator of Pi excretion in the growing rats, since it can markedly alter the acute phosphaturic response to parathyroid hormone.

Animals↗