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101.
S. Fermandjian S. Tran-Dinh J. avrda E. Sala R. Mermet-Bouvier E. Bricas P. Fromageot 《Biochimica et Biophysica Acta (BBA)/General Subjects》1975,399(2)
The 13C chemical shifts of several 85% 13C-enriched amino acids and small peptides were studied as a function of pH. The results show that the chemical shifts of carbon atoms of ionizable groups vary significantly within the zone of their pK. Generally with the pH going from 7 to 1 all the δC are shifted more or less upfield with the exception of the carbonyl group of the second last residue which is shifted slightly downfield. This suggests the formation of an hydrogen bond at acid pH involving in a seven-membered ring the C=O in question and the COOH terminal.The percentage of cis and trans conformers of glycyl-l-proline and glycyl-l-prolylglycine were studied as a function of pH. The trans form is always preponderant whatever the pH. The accessibility of the carbonyl group to protonation of the proline residue strongly influences the cis-trans equilibrium. Thus, with the pH varying from 7 to 1, the trans isomer changes from 61 to 85% for glycyl-l-proline and only from 77 to 80% for glycyl-l-prolylglycine.The proton NMR studies underline the important differences existing between the two molecular forms of glycyl-l-proline. The cis conformation is characterized with regard to the trans form by the non-equivalence of the α-protons of the glycine residue, by a lower pK1 and by a larger ΔδHα of the proline residue as a function of pH. These results could suggest an end-to-end interaction in the cis form of the glycyl-l-proline molecule.The 13C-13C coupling constants were also studied as a function of pH. The results show that JCo-Cα of a C-terminal residue, varying from 5 to 6 Hz and reflecting the pK of the carboxylate group, is a linear function of δCo and δCα as in the case of the amino acids. The total variation of the electron density of those two carbons in an amino acid is approximately 40% weaker than in a C-terminal residue. The charge distribution along the Cα−Co bond, however, is practically the same in both cases.Finally the ratios of the conversion rate constants of the two isomers cis-trans of glycyl-proline were calculated at different pH values; the relations between the isomer percentages and δCo, δCα on the one hand and the JCo-Cα on the other were established. 相似文献
102.
Mark L. Johnson Joell B. Hansen James C. Donofrio Carlo M. Veneziale 《Biochimica et Biophysica Acta (BBA)/General Subjects》1981,675(1):140-142
Dexamethasone in the medium perfusin isolated rabbit livers caused a fast-acting and reversible effect on liver pyruvate kinase. The effect was to lower th assayable V activity (units/g tissue) without changing the concentration (nmol/g enzyme protein). In effect, glucocorticoid lowered the specific activity (units/nmol of enzyme) by direct action on liver. The effect on liver pyruvate kinase is mediated by a relatively stable alteration; 30 min after perfusate (with steroid) was replaced by perfusate (without steroid), the effect remained strongly evident. 相似文献
103.
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105.
Abstract The presence, in the North Adriatic sea and in the Chioggia and Marano lagoons, of Pseliodinium vaubanii a rare dinoflagellate species, is reported. Our results showed that Pseliodinium vaubanii is a very frequent and abundant species in these environments. 相似文献
106.
Differential inactivation of plant lauric acid omega- and in-chain-hydroxylases by terminally unsaturated fatty acids 总被引:1,自引:0,他引:1
J P Salaün A Simon F Durst N O Reich P R Ortiz de Montellano 《Archives of biochemistry and biophysics》1988,260(2):540-545
The microsomal fraction from Vicia sativa L. cv. Septimane contains a cytochrome P-450-dependent lauric acid omega-hydroxylase that is inactivated in a time-dependent, pseudo-first-order manner when the microsomes are incubated with 11-dodecynoic acid. The rate constant for the inactivation is approximately 4.3-4.8 X 10(-3) s-1. In contrast, the olefinic analog 11-dodecenoic acid is primarily a time-independent inhibitor of the omega-hydroxylase. 1-Aminobenzotriazole, 3-phenoxy-1-propyne, and 3-(2,4-dichlorophenoxy)-1-propyne, mechanism-based inactivators of cinnamic acid 4-hydroxylase, and 9-decenoic acid, a mechanism-based inactivator of the lauric acid in-chain hydroxylase, are at best poor inactivators of the omega-hydroxylase. Conversely, cinnamic acid 4-hydroxylase is only slightly affected by concentrations of 11-dodecynoic acid that completely inactivate the omega-hydroxylase. 11-Dodecynoic acid is thus a potent, relatively specific, inactivator of the V. sativa lauric acid omega-hydroxylase. 相似文献
107.
Castellani Valentina Sanyé-Mengual Esther Sala Serenella 《The International Journal of Life Cycle Assessment》2021,26(10):2040-2055
The International Journal of Life Cycle Assessment - Current patterns of household goods consumption generate relevant environmental pressures and impacts. Environmental impacts are not only... 相似文献
108.
Sala Serenella Amadei Andrea Martino Beylot Antoine Ardente Fulvio 《The International Journal of Life Cycle Assessment》2021,26(12):2472-2473
The International Journal of Life Cycle Assessment - 相似文献
109.
Abstract Uptake of Phosporus-P32 by CUSCUTA EPITHYMUM parasitic of TRIFOLIUM REPENS. — Filaments of C. epithymum, parasitic on T. repens, partially immersed in a solution containing KH2P32O4, uptake from the host solely, or mainly, radioactive ortophosphate. Radioactive hexose phosphates and radioactive nucleotides present in the extracts prepared from C. epithymum, appear to be the result of the metabolization by the dodder of the orthophosphate uptaken from the host. 相似文献
110.
ABSTRACT A phytosociological study of the shrubland communities which colonise abandoned terraced olive groves in the Tyrrhenian district of Central Italy is presented here. The vegetational analysis was carried out using the Braun Blanquet phytosociological approach. Two main types of shrubland communities characterising distinct environmental conditions occur within abandoned terraced olive groves. On the one hand, there are those scrub types which tend to occupy the central part of the terrace; on the other hand, there are the scrubs types which develop along the stone walls bordering the terrace. Different phytosociological associations, sub-associations, and variants ranging from Pistacio-Rhamnetalia alaternii to Prunetalia spinosae are recognised and described. In the warm dry areas, both Myrto-Lentiscetum and Rhamno-Euphorbietum dendroidis occur. Also, a new Oleo-Ceratonion sub-association (Myrto-Lentiscetum spartietosum junceii) is presented here for the first time. In the inner zones of the study area, a range of aspects characterising a new Pruno-Rubion ulmifolii community type (Roso-Rubetum ulmifolii ass. nova) are identified. 相似文献