ISSN:0008-4018    

DOI:10.1139/o81-001

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The Mg2+-dependent phosphatidate phosphohydrolase activity increased in the microsomal and decreased in the soluble fraction of isolated rat fat cells incubated for short periods with the lipolytic hormones or agents, epinephrine, cyclic AMP, theophylline, and dibutyryl cyclic AMP. Adrenocorticotropin, on the other hand, increased not only the microsomal but also the soluble activity. The increases in microsomal activity ranged from 30 to 134% with epinephrine to almost 200% with dibutyryl cyclic AMP. The decreases in soluble activity were more modest. The effect of epinephrine was inhibited by the β-adrenergic antagonist propranolol while the α-antagonist phentolamine enhanced it. These results strongly suggest that the fat cell phosphatidate phosphohydrolase is controlled through the β-adrenergic receptor and the activity of adenylate cyclase. Lipolysis, as measured by fatty acid release, was stimulated in a similar pattern as the microsomal activity suggesting parallel activation of the hormone sensitive lipase and phosphatidate phosphohydrolase. It is speculated that the activation of this lipogenic enzyme by lipolytic stimuli may represent a mechanism whereby fatty acid release from adipose tissue may be modulated and intracellular fatty acid accumulation maybe counteracted during accelerated lipolysis in adipose tissue.

ISSN:0008-4018    

DOI:10.1139/o81-002

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The binding of the chloroplast coupling factor CF1to lipid vesicles was analyzed by gel filtration. CF1can be bound to vesicles made of chloroplast lipids but not of lecithin. The presence in the vesicle walls of a proteolipid subunit of the hydrophobic component of the coupling factor increases the binding of CF1. The apparent binding constant and the maximum protein/lipid ratio are calculated. The Ca2+-ATPase activity of bound CF1is markedly lower than that of dissolved CF1. It is confirmed that the proteolipid is aN,N′-dicylohexylcarbodiimide sensitive proton channel. The binding of CF1on proteolipid vesicles decreases their proton permeability.

ISSN:0008-4018    

DOI:10.1139/o81-003

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Chromatin appears to undergo structural modification after replication and before integration into bulk chromatin. In ascites cells, postreplicated chromatin displays a transient resistance to digestion with micrococcal nuclease. This resistance may be correlated with a shorter DNA repeat length (178 base pairs) than that found in bulk chromatin (187 base pairs). Selective labelling or selective digestion of DNA sequence classes could not account for these observations. In both bulk and postreplicated chromatin, three electrophoretic types of mononucleosomes were found. Postreplicated mononucleosome types showed selective sensitivities to nuclease digestion whereas bulk mononucleosome types did not.

ISSN:0008-4018    

DOI:10.1139/o81-004

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

[3H]Pargyline has been covalently linked to active sites of both type A and type B monoamine oxidase (MAO) obtained from various tissues. Rat heart and human placenta were chosen to represent predominantly type A MAO, pig and bovine livers to represent type B MAO, and rat liver and brain to represent mixed type A and type B MAO’s. The [3H]pargyline–MAO adducts were isolated and hydrolyzed by proteolytic enzymes, and the labelled peptides (pargyline-binding sites) separated and compared by paper chromatography and by paper electrophoresis at various pH values. Only one common pargyline peptide was obtained from all the different MAO’s. The alternative A and B sites were assessed after preincubation of rat liver MAO with the selective inhibitors deprenyl (to block the B site) and clorgyline (to block the A site). Following proteolysis of the [3H]pargyline peptides of both type A and type B MAO from this pretreated rat liver, MAO has been purified by a series of chromatographic and electrophoretic procedures. Micro-Edman degradation, followed by dansylation, revealed the amino acid sequence to be Ser-Gly-Gly-Cys(X)-Tyr. It is concluded that the primary structures immediately surrounding the pargyline-binding sites are identical for both type A and type B MAO in these tissues.

ISSN:0008-4018    

DOI:10.1139/o81-005

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The mechanism by which Semliki Forest virus inhibits the incorporation of [methyl-3H]- choline into phosphatidylcholine has been investigated. Decreased labeling of the lipid was not due to altered uptake of [methyl-3H]choline. The specific activities of choline kinase and CTP:phosphocholine cytidylyltransferase were unchanged. The previously observed inhibition (Vance, D. E. &Burke, D. C. (1974)Eur.J.Biochem.43, 327–336) of CDP-choline:1,2-diacylglycerol phosphocholinetransferase was confirmed. Since the decreased activity of the phosphocholinetransferase may not have caused the reduced labeling of phosphatidylcholine, the amounts of this lipid and its precursors were measured. We observed changes in the concentration of phosphocholine (34 ± 12 and 120 ± 40 nmol∙g cells−1in mock- and virus infected cells, respectively) and CTP (116 ± 35 and 36 ± 13 nmol∙g cells−1in mock- and virus-infected cells, respectively). Pulse–chase studies with [methyl-3H]choline demonstrated that, initially, most of the radioactivity was in phosphocholine. As it disappeared from this compound, it appeared in phosphatidylcholine. From these results, we calculated the rate of phosphatidylcholine biosynthesis to be 0.56 and 1.23 nmol∙min−1∙g cells−1in mock- and virus-infected BHK-21 cells, respectively. We conclude that phosphatidylcholine biosynthesisis not inhibited in Semliki Forest virus infected BHK cells, but rather is stimulated 6.75 h after infection. The decreased labeling observed during pulse studies with [methyl-3H]choline is due to dilution of the labeled choline into a pool of phosphocholine which is 3.5 times larger in the infecte

ISSN:0008-4018    

DOI:10.1139/o81-006

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The association between hepatic microsomal enzyme induction and triacylglycerol metabolism was examined in fasting male guinea pigs injected intraperitoneally with 50 mg phenobarbital∙kg−1for 7 days. Enzyme induction was established by a significant increase in hepatic aminopyrineN-demethylase activity, cytochrome P450 content, and hepatic γ-glutamyltransferase activity. Increased activity of γ-glutamyltransferase was also observed in the blood serum of treated animals. The phenobarbital-treated guinea pigs manifested increased hepatic triacylglycerol content and serum triacylglycerol concentration, accompanied by enhanced ability of cell-free fractions of liver to synthesize glycerolipidsin vitrofromsn-[14C]glycerol 3-phosphate and fatty acids. Microsomal phosphatidate phosphohydrolase accounted for 97% of the total liver activity of this enzyme, and its specific activity was 50-fold higher than that of the cytosolic enzyme when each was measured under optimal conditions. Activity of the cytosolic phosphohydrolase per liver doubled and that of the microsomal phosphohydrolase increased by 40% in the phenobarbital-treated guinea pigs. The microsomal, but not the cytosolic enzyme, showed a significant correlation with hepatic triacylglycerol content. Significant correlation was observed between the various parameters of hepatic microsomal enzyme induction and hepatic triacylglycerol content, suggesting that enzyme induction may promote triacylglycerol synthesis and consequent hypertriglyceridaemia in the guinea pi

ISSN:0008-4018    

DOI:10.1139/o81-007

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The experimental observations of Welbourne (Am.J.Physiol.226, 544–548 (1974)) led him to propose that a γ-glutamyltransferase activity contributes significantly to basal renal ammonia production. He measured the transferase activityin vitroas γ-glutamylhydroxamate or ammonia production from glutamine and hydroxylamine. We report that in crude homogenates of rat kidney, γ-glutamyltransferase activity requires the presence of a divalent cation, arsenate, and ADP. These conditions are also required for the maximal expression of the γ-glutamyltransferase reaction catalyzed by glutamine synthetase. Glutamine synthetase and γ-glutamyltransferase activities exhibit an identical distribution during differential centrifugation. In addition, the two activities comigrate during sucrose gradient velocity centrifugation, and exhibit identical heat inactivation andL-methionine sulfoximine inhibition profiles. Further-more, both activities are found to be localized primarily in the outer stripe region of the renal medulla. Based on these observations, it is concluded that the primary γ-glutamyltransferase activity as assayed in rat renal tissue is a partial reaction of glutamine synthetase, an enzyme which does not catalyze the production of ammonia and γ-glutamyl peptides from glutamine.

ISSN:0008-4018    

DOI:10.1139/o81-008

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Mitochondria fromVigna sinensis(L.) Savi cv. Pitiuba contain the polyamines spermine, spermidine, and putrescine. The membrane-bound F1-ATPase from mitochondria ofVigna sinensisis activated by these polyamines at physiological concentrations. The effect of polyamines on the membrane-bound F1-ATPase is dependent on the concentrations of Na+, K+, MgATP, and Mg2+. Excess Na+or K+prevents the activation of the membrane-bound F1-ATPase by spermine and spermidine, but not by putrescine. The most pronounced effects were observed at low MgATP concentrations in the absence of Na+and K+. At [MgATP] = 0.08 mM, spermine activation of the membrane-bound F1-ATPase was 130%.The membrane-bound F1-ATPase is slightly activated by Mg2+at lower concentrations and strongly inhibited by Mg2+at higher concentrations. Activation as well as inhibition is dependent on the substrate MgATP concentration. Although there is competition between Mg2+and MgATP, the binding sites for these two ligands are different (pseudocompetitive inhibition). The inhibition of the membrane-bound F1-ATPase can be reversed by polyamines. There is evidence that the binding sites for Mg2+and polyamines are identical.The F1-ATPase detached from the membrane is neither activated by polyamines nor inhibited by Mg2+. Therefore, the binding sites for Mg2+and polyamines seem to be localized on the membrane.

ISSN:0008-4018    

DOI:10.1139/o81-009

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The protein synthesis response ofChironomus tentanssalivary glands to a heat shock was analyzed by means of [3H]leucine pulse labeling, sodium dodecyl sulfate – polyacrylamide slab gels, and fluorography. Seven new cytoplasmic polypeptides with relative masses (Mr) of 90 000), 76 000, 73 000, 68 000, 28 000, 25 000, and 22 000 are synthesized in response to a39 °C heat shock (HS) while the synthesis of most of the normal proteins is reduced. The major HS-induced protein is the 68 000 species. The length of the heat treatment does not modify markedly the pattern of induced proteins but the temperature has an effect: while the responses at 37 and 39 °C are similar, two HS-induced polypeptides (Mr90 000 and 76 000) are not seen after a treatment at 41 °C. Kinetic studies of the response show an asynchrony in the appearance of the various HS proteins indicating that their individual rates of synthesis differ or that their induction is not fully coordinated. No significant differences were found between the protein patterns of a mitochondria-rich cytoplasmic zone obtained by microdissection and the whole cytoplasm, but two heat-induced proteins are present in the microdissected nuclei: a 68 000 polypeptide, comigrating with the major cytoplasmic one, and a 34 000 protein, almost exclusively seen in the nucleus.

ISSN:0008-4018    

DOI:10.1139/o81-010

出版商:NRC Research Press    

年代:1981

数据来源: NRC