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11.
Photoconversion of 7-dehydrocholesterol to vitamin D3 in synthetic phospholipid bilayers 总被引:1,自引:0,他引:1
The incorporation of 7-dehydrocholesterol into synthetic phospholipid bilayers altered the distribution of products after photolysis. In liposomes, the relative amounts of 7-dehydrocholesterol and lumisterol were elevated, and tachysterol was reduced from the levels observed in hexane solution. Z to E isomerization of the previtamin to tachysterol is favored in organic solvents. The inhibition of this process is evidence that an ordered lipid matrix places a new constraint on the conformation of the ring B fission product--one in which the configuration is favorable for a return to a cyclized diene. Further, rate enhancements of up to 15-fold were observed for the thermal isomerization of the previtamin to vitamin D3 in liposomes. The free energies of activation for the reaction at 25 degrees C were reduced by 1.3-1.5 kcal/mol in the bilayer environment compared to that of hexane. As this reaction involves the concerted transfer of a hydrogen via a cyclic intermediate, it provides additional evidence for membrane stabilization of an all-cis conformation of the previtamin. Photoproduct ratios were also studied for 7-dehydrocholesterol adsorbed to a variety of solid supports. That nonspecific interactions of 7-dehydrocholesterol with lipid can influence product formation may have important implications with respect to the mechanism of vitamin D3 biosynthesis. 相似文献
12.
13.
Uncharged poly(Nε-methyl-L -lysine) (PMLL) and its isomer, poly(Nδ-ethyl-L -ornithine) (PELO), in alkaline solution (pH ca. 12) undergo a helix-to-β transition upon mild heating at 50°C or higher in a manner similar to that of poly(L -lysine) (PLL). The rate of conversion follows the order: PMLL < PELO < PLL. The helix can be regenerated upon cooling near zero degrees, for instance, after more than 12 hr at 2°C. At concentrations less than 0.02% the β form is intramolecular, but at higher concentrations both intra- and intermolecular β forms are generated. Poly(Nδ-methyl-L -ornithine) (PMLO), an isomer of PLL, behaves like poly(L -ornithine); uncharged PMLO in alkaline solution is partially helical and becomes disordered at elevated temperatures. 相似文献
14.
Sixteen enzymatic and non-enzymatic proteins of the pigeon Columba livia domestica were examined electrophoretically. These proteins were presumed to be under control by 22 loci. Of the 22 loci, 6 were defined as polymorphic and 15 as monomorphic. Another locus was variable, but the variation was not genetically interpretable. Average heterozygosity calculated over 21 loci was 0.075. 相似文献
15.
16.
K Yoshida T Sakurada H Kitaoka H Fukazawa N Kaise K Kaise M Yamamoto S Saito K Yoshinaga 《Endocrinologia japonica》1983,30(2):211-217
Monodeiodination of T4 to T3 and rT3 in the intact cells of dog renal tubuli and glomeruli was investigated. The tubuli and glomeruli were obtained by a sieve method. T4 (2 micrograms/ml) was incubated in Tris-HCl buffer, pH 7.5, with renal cells (180 micrograms protein/ml) and 5 mM DTT for 1 h at 37 degrees C and the T3 and rT3 generated during incubation were measured by specific radioimmunoassays. In order of decreasing activity, dog renal cortical tubuli, cortical homogenate, glomeruli and medullary tubuli were capable of converting T4 to T3. Net rT3 production from T4 in cortical tubuli was also greater than that in cortical homogenate. The conversion of T4 to T3 and also to rT3 in cortical tubuli was enzymatic in nature, since the reactions showed dependence on time and protein concentration; instability to heating; temperature and pH optimum. The production of T3 and rT3 from T4 was maximum at pH 6.5 and at pH 9.5, respectively, indicating that two different enzymic systems, a 5- and a 5'-monodeiodinase, might be involved in the deiodination of the tyrosyl and the phenolic ring of T4 in dog kidney. 相似文献
17.
Nucleotide sequence of the PR-1 gene of Nicotiana tabacum 总被引:7,自引:0,他引:7
M Ohshima M Matsuoka N Yamamoto Y Tanaka Y Kano-Murakami Y Ozeki A Kato N Harada Y Ohashi 《FEBS letters》1987,225(1-2):243-246
A gene encoding one of the pathogenesis-related proteins, PR1a, and two related pseudogenes were isolated from Nicotiana tabacum. The cloned PR1a gene (pPR-gamma) and one of the pseudogenes (pPR-alpha) were sequenced and found to have similar structures. The sequence of pPR-gamma was quite similar to that of the cDNA clone of PR1a. The plasmid pPR-gamma did not contain an intron and had a typical promoter sequence in the 5'-flanking region. 相似文献
18.
Human skeletal muscle contains two major aminopeptidases: an anion-activated aminopeptidase B and an aminopeptidase M-like enzyme 总被引:1,自引:0,他引:1
S Ishiura T Yamamoto M Yamamoto M Nojima T Aoyagi H Sugita 《Journal of biochemistry》1987,102(5):1023-1031
Two major aminopeptidases, an aminopeptidase B and an aminopeptidase M-like enzyme, were purified from human skeletal muscle by DEAE-cellulose, HPLC gel filtration, and hydroxyapatite column chromatographies. The purified aminopeptidase B exhibits a molecular weight of 76,000 under both native and denaturing conditions. The activity of the aminopeptidase B is regulated by C1 ions and other anions in vitro. On the other hand, the aminopeptidase M-like enzyme is a monomeric protein having a molecular weight of 96,000. It is capable of significantly cleaving Phe-, Leu-, Arg-, and Ala-aminoacyl bonds in the presence of 2-mercaptoethanol. The pH optima for both enzymes are around 7.0, and bestatin is an effective inhibitor of both enzymes. 相似文献
19.
20.
Changes in the activities of adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinases in response to prostaglandin (PG)E2-induced elevation of intracellular cAMP level were investigated with a murine macrophage-like cell line, P388D1. Photoaffinity labeling with 8-azido-[32P]cAMP showed that untreated P388D1 cells possess two types of cAMP-binding proteins of m.w. 49,000 and 52,000, respectively, in the cytosol fraction in a ration of 1:8. They must represent regulatory subunits (RI and RII, respectively) of cAMP-dependent protein kinases, because affinity chromatography on a column of omega-aminohexyl-agarose of the cytosol fraction clearly separated two fractions that exhibited the enzymatic activities and cAMP-binding activities. Photoaffinity labeling of these fractions with 8-azido-[32P]cAMP confirmed the separation of two types of isoenzymes, because each cAMP-dependent protein kinase active fraction was associated with only one type of regulatory subunit. The exposure of P388D1 cells to exogenously added PGE2 (1 microM) caused about 7.5-fold increase in the intracellular cAMP level within 30 sec. The cAMP level then sharply dropped to about 100 pmol/10(7) cells, remained at this level for about 20 min, and then gradually increased to 200 pmol/10(7) (about fivefold over the control). The enzyme assay of the cytosol demonstrated that the activation of cAMP-dependent protein kinases closely follows the kinetics of the intracellular cAMP level. The activation of the enzyme was specific for PGE2 and was not triggered by 1 microM PGF2 alpha or PGD2 which have been shown to be unable to activate adenylate cyclase of P388D1 cells. The PGE2-induced increase in the intracellular cAMP level appeared to activate preferentially the type I isoenzyme, inasmuch as the enzymatic activity of this type separated by the affinity chromatography of the cytosol of PGE2-exposed cells was lower in the presence than in the absence of cAMP, whereas the type II enzyme activity remained responsive to exogenously added cAMP. 相似文献