Some properties of histidine:pyruvate transaminase (HPT) and phenylalanine:pyruvate transaminase (PPT) in the cytosol of rat liver were studied. HPT and PPT activity could not be separated by DEAE-Sephadex A-50 or hydroxylapatite column chromatography, and the ratio of activity remained constant during these purification procedures. The two enzyme activities also showed similar heat stability and responses to glucagon injection. Based on these findings, we suggest that a single enzyme may specifically catalyze histidine:pyruvate and phenylalanine:pyruvate transamination. 相似文献
High density lipoproteins were isolated from plasma of white Leghorn hens by ultracentrifugal flotation between densities 1.063 and 1.210 g/ml. After delipidation, the lipid-free proteins were fractionated by chromatography on Sephadex G-150 in urea; one major apolipoprotein was isolated and characterized. From its chemical, physical and immunochemical properties, the major apoprotein from hen high-density lipoproteins has characteristics similar to the major apoprotein of human high density lipoproteins, apoA-I. Thus the hen protein has been designated hen apoA-I. Hen apoA-I has a molecular weight of approximately 28 000 as determined by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. Its calculated molecular weight from its 234 constituent amino acids is 26 674. Hen apoA-I differed from its human counterpart by containing isoleucine. Treatment of hen apoA-I with carboxypeptidase A yielded a COOH-terminal sequence of Leu-Val-Ala-Gln. Automatic Edman degradation of the apoprotein gave an NH2-terminal sequence of Asp-Glu-Pro-Gln-Pro-Glu-Leu. Hen apoA-I had a circular dichroic spectrum typical of alpha-helical structures; the calculated helicity was 90%. Goat antisera prepared to hen apoA-I formed precipitin lines of complete identity to the hen apoprotein but lines of only partial identity to human apoA-I. These studies show that the major apoprotein from hen and human high-density lipoproteins have similar properties to each other suggesting a common physiologic function. 相似文献
(1) The ATPase inhibitor protein has been isolated from rat liver mitochondria in purified form. The molecular weight determined by sodium dodecyl sulfate gel electrophoresis is approximately 9500, and the isoelectric point is 8.9.
(2) The protein inhibits both the soluble ATPase and the particle-bound ATPase from rat liver mitochondria. It also inhibits ATPase activities of soluble F1, and inhibitor-depleted submitochondrial particles derived from bovine heart mitochondria.
(3) On particle-bound ATPase the inhibitor has its maximal effect if incubated in the presence of Mg2+. ATP at slightly acidic pH.
(4) The inhibitor has a minimal effect on Pi-ATP exchange activity in sonicated submitochondrial particles. However, unexpectedly the inhibitor greatly stimulates Pi-ATP exchange activity in whole mitochondria while the low ATPase activity of the mitochondria is not affected. The possible mechanism of action of the inhibitor on intact mitochondria is offered. 相似文献
Two glycopeptides present in equal amounts were isolated from a pronase digest of alpha1-protease inhibitor of human plasma by gel filtration on Sephadex G-50 and chromatography on DEAE-cellulose. The carbohydrate side chains in both glycopeptides are linked through asparaginyl residues. The glycopeptides were digested sequentially with specific glycosidases; and after each step, the released sugars as well as the composition of the residual peptides were determined. The linear structures of these glycopeptides deduced from these data are shown below. Based on the total carbohydrate content of the intact protein and with these structural data, it is postulated that 4 oligosaccharide units are attached to 1 molecule of the protein; 2 of these were represented as in Equation 1, the other 2 as in Equation 2. 相似文献
The role of the adrenal gland in suppressing the onset of maternal behavior in virgin female rats was investigated. Virgin female rats were either ovariectomized, adrenalectomized, or subjected to the combined operation and tested for the induction of maternal behavior by being exposed to young pups. Females that were both ovariectomized and adrenalectomized 4 weeks prior to testing exhibited significantly shorter latencies to the onset of maternal behavior than that of females subjected to either ovariectomy or adrenalectomy alone. Replacement of either estrogen or progesterone in the group that was both adrenalectomized and ovariectomized resulted in a prolongation of the average latency to become maternal. The results indicated that both estrogen and progesterone can act to inhibit the onset of maternal behavior and that the adrenal gland may act to suppress the onset of such behavior by supplying an extra-ovarian source of endogenous progesterone and estrogen. 相似文献
1. A new procedure is described for selecting nitrogenase-derepressed mutants based on the method of Brenchley et al. (Brenchley, J.E., Prival, M.J. and Magasanik, B. (1973) J. Biol. Chem. 248, 6122-6128) for isolating histidase-constitutive mutants of a non-N2-fixing bacterium. 2. Nitrogenase levels of the new mutants in the presence of NH4+ were as high as 100% of the nitrogenase activity detected in the absence of NH4+. 3. Biochemical characterization of these nitrogen fixation (nif) derepressed mutants reveals that they fall into three classes. Three mutants (strains SK-24, 28 and 29), requiring glutamate for growth, synthesize nitrogenase and glutamine synthetase constitutively (in the presence of NH4+). A second class of mutants (strains SK-27 and 37) requiring glutamine for growth produces derepressed levels of nitrogenase activity and synthesized catalytically inactive glutamine synthetase protein, as determined immunologically. A third class of glutamine-requiring, nitrogenase-derepressed mutants (strain SK-25 and 26) synthesizes neither a catalytically active glutamine synthetase enzyme nor an immunologically cross-reactive glutamine synthetase protein. 4. F-prime complementation analysis reveals that the mutant strains SK-25, 26, 27, 37 map in a segment of the Klebsiella chromosome corresponding to the region coding for glutamine synthetase. Since the mutant strains SK-27 and SK-37 produce inactive glutamine synthetase protein, it is concluded that these mutations map within the glutamine synthetase structural gene. 相似文献
Intracellular cAMP levels determined by radioimmunoassay technique were compared in normal rat mammary gland and DMBA-induced mammary adenocarcinoma as well as in epithelial cells derived from these tissues and grown in monolayer cultures. It was found that cAMP levels were higher in mammary tumors (0.643 p mole/mg wet weight) than in normal gland (0.158 p mole/mg). In contrast, cAMP levels in cultured adenocarcinoma cells were lower than those in normal mammary epithelial cells. The apparent contradiction may be a consequence of the fact that cAMP values represent the average value of the composite cell types and not the epithelial components in question. 相似文献
Two intensely mauve UV fluorescent compounds isolated from Tagetes root were found to be phototoxic to Candida albicans. By chromatography on alumina followed by gel filtration on Sephadex LH-20, the compounds were identified as 5-(3-buten-1-ynyl)-2,2′-bithienyl and α-terthienyl. 相似文献