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A Pascal

Publications and source records attributed to A Pascal.

At least 19 recordsLinked to original sources
PubMed2001

Beta-carotene redox reactions in photosystem II: electron transfer pathway.

A carotenoid (Car), a chlorophyll (Chl(Z)), and cytochrome b(559) (Cyt b(559)) are able to donate electrons with a low quantum yield to the photooxidized chlorophyll, P680(+), when photosystem II (PSII) is illuminated at low temperatures. Three pathways for electron transfer from Cyt b(559) to P680(+) are considered: (a) the "linear pathway" in which Cyt b(559) donates via Chl(Z) to Car, (b) the "branched pathway" in which Cyt b(559) donates via Car and where Chl(Z) is also able to donate to Car, and (c) the "parallel pathway" where Cyt b(559) donates to P680 without intermediate electron carriers and electron donation from Chl(Z) and Car occurs by a competing pathway. Experiments were performed using EPR and spectrophotometry in an attempt to distinguish among these pathways, and the following observations were made. (1) Using PSII with an intact Mn cluster in which Cyt b(559) was preoxidized, Car oxidation was dominant upon illumination at < or =20 K, while electron donation from Chl dominated at >120 K. (2) When Cyt b(559) was prereduced, its light-induced oxidation occurred at < or =20 K in what appeared to be all of the centers and without the formation of a detectable Car(+) intermediate. The small and variable quantity of Car(+) photoinduced in these experiments can be attributed to the residual centers in which Cyt b(559) remained oxidized prior to illumination. (3) The relative rates for irreversible electron donation from Cyt b(559) and Car were determined indirectly at 20 K by monitoring the flash-induced loss of charge separation (i.e., the accumulation of Cyt b(559)(+)Q(A)(-) or Car(+)Q(A)(-)). Similar yields per flash were observed (13% for Cyt b(559) and 8% for Car), indicating similar donation rates. The slightly lower yield with Car as a donor is attributed at least in part to slow charge recombination occurring from the Car(+)Q(A)(-) radical pair in a fraction of centers. (4) Light-induced oxidation of Cyt b(559) and Car at 20 K was monitored directly by EPR, and the rates were found to be indistinguishable. The parallel pathway predicts that when both Cyt b(559) and Car are prereduced, the relative amounts of Cyt b(559)(+) and Car(+) produced upon illumination at 20 K should depend directly on their relative electron donation rates. The measured similarity in the donation rates thus predicts comparable yields of oxidation for both donors. However, what is observed experimentally is that Cyt b(559) oxidation occurs almost exclusively, and this argues strongly against the parallel pathway. The lack of Car(+) as a detectable intermediate is attributed to rapid electron transfer from Cyt b(559) to Car(+). The trapping of Car(+) at low temperature when Cyt b(559) is preoxidized but its absence when Cyt b(559) is prereduced is taken as an argument against the simple linear pathway. Overall, the data reported here and previously favor the branched pathway over the linear pathway, while the parallel pathway is thought to be unlikely. Structural considerations provide further arguments in favor of the branched model.

Carotenoids↗
PubMed2001

Pigment conformation and pigment-protein interactions in the reconstituted Lhcb4 antenna protein.

Resonance Raman spectra of the native Lhcb4 antenna protein are compared with those of a recombinant protein prepared by in vitro refolding of its polypeptide, over-expressed in Escherichia coli, with added pigments [Giuffra et al. (1996) Eur. J. Biochem. 238, 112-120]. The results indicate that the native pigment conformation is reproduced almost perfectly in the reconstituted protein, with only small differences which are attributed to a slight shift in the Soret absorption peak of two or more chlorophylls. This procedure therefore represents a model system for the investigation of site-directed mutant LHC proteins, which are otherwise very difficult to obtain.

Carotenoids↗
PubMed2001

Cloning and developmental expression of STAT5 in Xenopus laevis.

Transcription factors of the signal transducer and activator of transcription (STAT) family are required for cellular responses to multiple signalling molecules. After ligand binding-induced activation of cognate receptors, STAT proteins are phosphorylated, hetero- or homodimerize, and enter the nucleus. STAT dimers bind to specific DNA elements and alter the transcriptional activity of the signal-responsive genes. We report the cloning and developmental pattern of expression of XSTAT5, a Xenopus laevis member of the STAT family, closely related to the mammalian STAT5A and STAT5B. XSTAT5 is expressed maternally and zygotically. With the onset of neurulation, XSTAT5 RNA are clearly localized in the anterior neural plate and subsequently in the neural structures of the developing eye, the pineal gland and the cement gland anlage. At late tailbud stages, a faint expression is detected in a ventral location that might correspond to the ventral blood islands.

Amino Acid Sequence↗
PubMed2000

Pigment binding site properties of two photosystem II antenna proteins. A resonance raman investigation.

Two light-harvesting proteins associated with photosystem II of higher plants, namely the major antenna complex LHCIIb and the minor Lhcb4 protein (CP29), have been investigated by resonance Raman spectroscopy. One of the two chlorophylls b and up to five of the six chlorophylls a present in Lhcb4 are shown to adopt similar binding conformations to the (presumably) corresponding molecules in LHCIIb, whereas at least two chlorophylls in the former protein assume unique conformations relative to the bulk complex. The overall conformation of bound xanthophyll molecules is identical in the two antenna proteins, although some small differences are apparent. The pigment binding properties of these two LHCs are discussed, with particular reference to possible structural motifs within this extended family of proteins.

Binding Sites↗
PubMed1999

Carotenoid oxidation in photosystem II.

The oxidation of carotenoid upon illumination at low temperature has been studied in Mn-depleted photosystem II (PSII) using EPR and electronic absorption spectroscopy. Illumination of PSII at 20 K results in carotenoid cation radical (Car+*) formation in essentially all of the centers. When a sample which was preilluminated at 20 K was warmed in darkness to 120 K, Car+* was replaced by a chlorophyll cation radical. This suggests that carotenoid functions as an electron carrier between P680, the photooxidizable chlorophyll in PSII, and ChlZ, the monomeric chlorophyll which acts as a secondary electron donor under some conditions. By correlating with the absorption spectra at different temperatures, specific EPR signals from Car+* and ChlZ+* are distinguished in terms of their g-values and widths. When cytochrome b559 (Cyt b559) is prereduced, illumination at 20 K results in the oxidation of Cyt b559 without the prior formation of a stable Car+*. Although these results can be reconciled with a linear pathway, they are more straightforwardly explained in terms of a branched electron-transfer pathway, where Car is a direct electron donor to P680(+), while Cyt b559 and ChlZ are both capable of donating electrons to Car+*, and where the ChlZ donates electrons when Cyt b559 is oxidized prior to illumination. These results have significant repercussions on the current thinking concerning the protective role of the Cyt b559/ChlZ electron-transfer pathways and on structural models of PSII.

Carotenoids↗
PubMed1999

Spectroscopic characterization of the spinach Lhcb4 protein (CP29), a minor light-harvesting complex of photosystem II.

A spectroscopic characterization is presented of the minor photosystem II chlorophyll a/b-binding protein CP29 (or the Lhcb4 protein) from spinach, prepared by a modified form of a published protocol [Henrysson, T., Schroder, W. P., Spangfort, M. & Akerlund, H.-E. (1989) Biochim. Biophys. Acta 977, 301-308]. The isolation procedure represents a quicker, cheaper means of isolating this minor antenna protein to an equally high level of purity to that published previously. The pigment-binding protein shows similarities to other related light-harvesting complexes (LHCs), including the bulk complex LHCIIb but more particularly another minor antenna protein CP26 (Lhcb5). It is also, in the main, similar to other preparations of CP29, although some significant differences are discussed. In common with CP26, the protein binds about six chlorophyll a and two chlorophyll b molecules. Two chlorophyll b absorption bands are present at 638 and 650 nm and they are somewhat more pronounced than in a recent report [Giuffra, E., Zucchelli, G., Sandonà, D., Croce, R., Cugini, D., Garlaschi, F.M., Bassi, R. & Jennings, R.C. (1997) Biochem. 36, 12984-12993]. The bands give rise to positive and negative linear dichroism, respectively; both show negative CD bands (cf. bands with similar properties at 637 and 650 nm in CP26). Chlorophyll a absorption is dominated by a large contribution at 674 nm which also shows similarities to the major band in LHCIIb and CP26, while (as for CP26) a reduction in absorption around 670 nm is observed relative to the bulk complex. Principal differences from LHCIIb and CP26, and from other CP29 preparations, occur in the carotenoid region.

Circular Dichroism↗
PubMed1997

[Value of a genetic evaluation before an intracytoplasmic sperm injection procedure].

Intracytoplasmic sperm injection (ICSI) still needs to be validated as far as safety is concerned. Results concerning foetal karyotypes currently seem to show an increase in sexual chromosomal abnormalities. In view of the heterogeneity of publications concerning genetic tests, it seems necessary to define a protocol with a limited time span, which will allow the extensive collection of data. The analysis of the results will secondarily allow a common procedure to be established. We propose a protocol limited in time, aiming to evaluate the chromosomal status at birth by a systematic karyotype of umbilical cord blood.

Adult↗
PubMed1996

[Poor responders followed for 3 years in an IVF program].

Our study consisted of a population of 100 women who represented an insufficient response to the induction of ovulation. We researched to find out which therapeutic approach, of the subsequent attempts to IVF would give greater hope to a better response. Two groups were individualized: in the first group (62 women) we obtained at least once, 3 oocytes (288 attempts), in the second group (38 women) we always obtained less than 3 oocytes. In the first group, in order to raise the pregnancy rate it was necessary to raise the rate of E2/oocyte. There fore raising the duration of stimulation and the quantity of ampullage of hMG. The long protocol, hMG, produced the best results. In the second group, the results were always worse it was more than a problem of protocol, it was a problem of the patients. In reality, the future of therapy for lower responsive patients is probably biological with hatching today and the possibilities with oocytary maturation in vitro in the near future.

Adult↗
PubMed1992

Medical care costs of intravenous drug users with AIDS in Brooklyn.

This article reports on a study of medical costs of intravenous drug users (IVDUs) with acquired immune deficiency syndrome (AIDS) in Brooklyn, NY, U.S.A. Sociodemographic and clinical data as well as information on medical resource use was gathered for 38 IVDUs with AIDS, all of whom belonged to minority racial/ethnic groups and were covered by Medicaid insurance. Data obtained through patient interviews and review of medical records indicated that the sample had mean annual medical charges of $33,002 per patient per year. Average inpatient charges were $24,171, with an average of 1.13 hospitalizations and 38.5 days of in-hospital care. Significantly more in-hospital care and higher inpatient charges on average were noted among patients who did not have a stable housing environment. Outpatient charges averaged $8,831, with 80% for pharmaceuticals. This estimate of medical charges and resource use, one of the first developed in a cohort of nonwhite individuals with i.v. drug use as a risk factor for human immunodeficiency virus infection, is about one third less than recent estimates reported from studies of cohorts of white homosexual men.

Acquired Immunodeficiency Syndrome↗
PubMed1991

The costs of AIDS in Los Angeles.

This article reports on the findings of a study of medical and non-medical expenditures of persons with acquired immune deficiency syndrome (AIDS) in Los Angeles in 1987 and 1988. Sociodemographic and clinical data as well as information on medical and nonmedical expenditures on 36 persons with AIDS were obtained through patient interviews and review of medical bills. Persons with AIDS required a mean of 1.6 hospitalizations per year and 17 days of in-hospital care. Mean charges for the first 12 months after diagnosis of AIDS were $22,272 for inpatient medical care and $22,850 for outpatient medical care. Overall, medical costs averaged $45,122 per patient per year with almost one-third of these costs devoted to outpatient pharmaceuticals, such as AZT and aerosolized pentamidine. Mean nonmedical costs of care for volunteer services, counselling, and in-kind assistance were $9,276. These results were similar to recently published estimates of medical costs of persons with AIDS. However, our data support changing problems of care for PWAs with increased use of outpatient medical care and pharmaceuticals and decreased use of in-hospital resources.

Acquired Immunodeficiency Syndrome↗