摘要:

Experiments were performed to study the effect of dietary sodium deficiency on thein vitrobiosynthesis of corticosteroids from tritiated cholesterol by homogenates of whole adrenal glands and on the properties of rat adrenocortical cytochrome P-450. Adrenal homogenates of rats kept on a sodium deficient diet for 17 days converted 3 times more tritiated cholesterol to corticosterone, 15 times more to 18-hydroxycorticosterone, and 6 times more to aldosterone than did homogenates from rats kept on the control diet. While adrenocortical cytochrome P-450 content did not differ significantly in the glands of experimental animals from that of control animals, changes could be observed in the cytochrome P-450 – carbon monoxide association time constants (KCO).

ISSN:0008-4018    

DOI:10.1139/o74-001

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

A comparison of the electrophoretic mobilities of the tryptic peptides of natural porcine motilin and a synthetic analogue with norleucine substituted for methionine revealed the absence of the acidic peptide TR3 of the natural material. Kinetic studies with leucine aminopeptidase and dansyl-Edman degradations on this peptide revealed the presence of glutamine at position 14 and not glutamic acid as previously reported. It is suggested that in the earlier preparation of natural porcine motilin deamidation of glutamine occurred.

ISSN:0008-4018    

DOI:10.1139/o74-002

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

17β-Estradiol-6,7-3H (E2), 17β-estradiol-6,7-3H-3-sulfate (E23S), and estriol-6,7-3H (E3) were each incubated with human kidney homogenates in the presence of uridine diphosphoglucuronic acid. Metabolites were purified by DEAE-Sephadex and Celite partition chromatography and were identified by crystallization with carrier steroid conjugates and free steroids. E2was converted to a small but definite extent (< 0.1–5%) to estrone-3-glucosiduronate, 17β-estradiol-3-glucosiduronate, and 17β-estradiol-17-glucosiduronate, the latter conjugate usually predominating. Under the experimental conditions E2was a better precursor of all three conjugates than was E23S. In one experiment where kidney cortex and medulla were incubated separately with E2, the former was some 20 times more efficient in glucosiduronate synthesis. E3was converted to the extent of 52–91% to estriol-16-glucosiduronate by whole kidney homogenates.

ISSN:0008-4018    

DOI:10.1139/o74-003

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

Labelled 17β-estradiol-3-glucosiduronate and 17β-estradiol-3-sulfate were both directly dehydrogenated to their respective 17-keto forms on incubation with human kidney homogenates. NAD increased the conversion to a greater extent than did NADP. The reverse reaction, even in the presence of NADH or NADPH was not found to a measurable extent, presumably because of rapid oxidation of the cofactors. High or low activity towards the conjugates was accompanied by high or low activity, respectively, towards free 17β-estradiol. These dehydrogenase activities were particularly high in the medulla of one kidney so investigated. Considerable sulfatase activity was usually encountered in these homogenates but little β-glucuronidase activity was demonstrated under the experimental conditions.

ISSN:0008-4018    

DOI:10.1139/o74-004

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

Both ρ+and ρ−strains ofSaccharomyces cerevisiaeaccumulate P503 during the early logarithmic phase of growth when cytochrome synthesis is repressed. Yeast cells grown on non-fermentable carbon sources (e.g. glycerol) did not accumulate P503. Cell-free extracts containing P503 were prepared from anaerobically grown (ρ+)S.cerevisiae. The addition to these extracts of mitochondria from ρ+cells grown aerobically on galactose caused the immediate disappearance of P503.Escherichia colirespiratory particles had a similar effect on P503. Mitochondrial preparations from ρ−cells or from anaerobically grown ρ+cells did not affect P503. Coprotetrahydroporphyrin III was not oxidized by aerobicS.cerevisiaemitochondria nor byE.colirespiratory particles.

ISSN:0008-4018    

DOI:10.1139/o74-005

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

Rat liver slices were incubatedin vitrowith sodium acetate-1-14C and the effect of some steroids on the incorporation of the substrate into digitonin precipitable sterols (DPS) was studied. Radioactive biosynthetic DPS was isolated from each incubate following digitonin precipitation, hydrolysis of the digitonide, and two silica gel thin-layer chromatographies. The following compounds were found to inhibit thein vitroDPS biosynthesis in this system: medroxyprogesterone acetate, norethynodrel, 17α-ethynyl estradiol, 17-hydroxy-progesterone, progesterone, and dehydroepiandrosterone.

ISSN:0008-4018    

DOI:10.1139/o74-006

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

γ-Glutamyl transpeptidase has been partially purified from kidneys of adult male rats by solubilization with deoxycholate and chromatography in the presence of Triton X-100. A new, sensitive assay has been developed to study the reaction of glutathione with methionine in the micromolar range. This assay was found to differ from those using γ-glutamylnaphthylamide as substrate in the activation of the enzyme by anions and cations, and in terms of the nature of the reaction catalyzed by the enzyme. The kinetics of the transpeptidation reaction have been studied with the substrates glutathione and methionine. The pattern of inhibition caused by the product cysteinylglycine suggested that the reaction was non-sequential. The Michaelis constants for glutathione and methionine were of the order of 40 μMand 3 mM, respectively.

ISSN:0008-4018    

DOI:10.1139/o74-007

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

Human amniotic fluid obtained by amniocentesis during the third trimester of pregnancy has been found to contain the enzyme for transferring galactose from UDP-galactose into various exogenous acceptors. The enzyme galactosyltransferase is present in soluble form and does not require Triton for activity. The optimum pH (pH 6.8), divalent cation requirement (Mn2+, 12.5 mM), optimum temperature (37 °C), and linearity with time and enzyme concentrations have been established. The amniotic fluid enzyme catalyzed the transfer of 60 nmol of galactose to fetuin acceptor per milliliter of amniotic fluid per hour and its apparentKmfor UDP-galactose is 9.1 × 10−5 M. The enzyme is stable to storage at −20 °C for at least 2 months. Acid hydrolysis and β-galactosidase treatment of the labelled reaction product released all of the radioactivity as14C-galactose. Uridine nucleotides inhibited the soluble enzyme whereas the adenine and cytidine nucleotides had no appreciable effect. The addition of α-lactalbumin in the assay caused the appearance of lactose synthetase activity and inhibition ofN-acetyllactosamine synthetase activity. The specific activity of the enzyme in the amniotic fluid in human and rat is 30- to 40-fold higher than in their serum. Placenta, fetal liver, and fetal lungs of rat also showed considerable enzyme activity.Enzymes that transferN-acetylglucosamine, sialic acid, andN-acetyl-4-galactosamine from their respective nucleotide sugars to exogenously added acceptors are also present in human amniotic fluid.

ISSN:0008-4018    

DOI:10.1139/o74-008

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

The activities and regulation of the enzymes of the synthetic pathway of branched-chain amino acids were investigated in the fission yeast,Schizosaccharomyces pombe. Previous studies had shown the presence of threonine deaminase (TD) and acetohydroxy acid synthetase (AHAS). The remaining isoleucine–valine enzymes, isomeroreductase (IR), dehydrase, and transaminase B, have now been characterized in cell-free extracts, indicating the presence in this yeast of the complete pathway as demonstrated in other microorganisms. α-Isopropylmalate synthetase (IPMS), the first enzyme of the leucine pathway, has properties of a typical regulatory enzyme; it is most active in the pH range 7.5–8.5, but is most sensitive to feedback inhibition byL-leucine at pH 6.5–7.0. Unlike the situation in baker's yeast, only AHAS and IR appeared to be subject to multivalent repression. TD was relatively resistant to any change in level, and AHAS was repressible by valine included in the growth medium. IPMS was repressed when cells were grown in complex medium; leucine alone did not cause repression, and in contrast with baker's yeast, neither did leucine plus threonine or a combination of all three branched-chain amino acids.

ISSN:0008-4018    

DOI:10.1139/o74-009

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

Oxytocin is hydrolytically cleaved in the presence of plasma oxytocinase to give an acyclic peptide, tyrosyl-isoleucyl-glutaminyl-asparaginyl-S-(S-cysteine)-cysteinyl-prolyl-leucyl-glycinamide (1,2-acyclic oxytocin). The synthesis of this peptide is described. It is shown to be of very low potency in milk-ejection-like activity and uterotonic activity. It does not inhibit the expression of these activities by oxytocin, suggesting that it does not interfere with the hormone's binding to target tissues. The presence of 1,2-acyclic oxytocin slightly inhibits the rate of degradation of oxytocin by plasma from pregnant women, in contrast to the marked inhibition of the degradation of cystine di-β-naphthylamide. TheKmfor the degradation of oxytocin is 30 times smaller than that of the degradation of cystine di-β-naphthylamide, which is of the same order as theKifor the inhibition of the degradation of cystine di-β-naphthylamide by 1,2-acyclic oxytocin. These results, together with information on the substrate specificity of plasma oxytocinase with respect to the N-terminal amino acid residue, suggest that there are molecular features of oxytocin other than its N-terminal residue that facilitate its interaction with plasma oxytocinase.

ISSN:0008-4018    

DOI:10.1139/o74-010

出版商:NRC Research Press    

年代:1974

数据来源: NRC