摘要:

Sarcolemma isolated from guinea pig heart binds calcium in an ATP-dependent manner. Sodium ions decrease the total amount of calcium bound by the membranes. ATP-dependent calcium binding is more sensitive to sodium than the non-ATP-dependent calcium binding. The ATPase active during calcium binding is affected by sodium ions to the same extent as the ATP-dependent calcium binding process. The inhibition of the calcium binding process and of ATPase activity by sodium was more pronounced when the membranes were preincubated with sodium. The effect of sodium on calcium binding is dependent on both the time of contact between sodium and the membranes and the concentration of sodium. It is suggested that the effect of sodium on the calcium binding system in the sarcolemma may be a link between the inhibition of Na+K+-ATPase (EC 3.6.1.3) by cardiac glycosides and the subsequent increase in intracellular calcium.

ISSN:0008-4018    

DOI:10.1139/o78-001

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The staphylococcal protease was coupled at the active-site serine residue with a spin-labeled analog of diisopropyl fluorophosphonate and the interaction of competitive inhibitors such as chloride and acetate anions, as well asN-carbobenzoxy-L-glutamic acid (Z-L-Glu), was investigated by electron paramagnetic resonance spectroscopy. It was observed that the addition of chloride ions to the spin-labeled enzyme increased the freedom of motion of the spin label while the presence of acetate ions and Z-L-Glu resulted in an increase in the immobilization of the spin label. These results suggest that these ions bind to the active site region in different ways.

ISSN:0008-4018    

DOI:10.1139/o78-002

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Paracoccus denitrificanswas grown in carbon-limited aerobic continuous culture (critical dilution rate (Dc) = 0.48 h−1). The molar growth yield for carbon (succinate or malate) was constant at about 60 over a broad dilution range (growth rate) from 0.10 to 0.48 h−1. Measurements of the stoichiometry of proton translocation associated with the oxidation of endogenous substrates yielded a ratio of protons ejected from the cell per atom of oxygen consumed (→H+:O) of 8.55 which decreased to 5.85 in the presence of piericidin A (PA), a specific inhibitor of NADH dehydrogenase (EC 1.6.99.3). With starved cells, the observed →H+:O associated with the oxidation of added succinate in the presence of PA was 5.61. These observed →H+:O's represent an underestimation since no correction was made for proton backflow during the short interval of respiratory activity. Aerobic growth ofPc.denitrificansin the chemostat becomes sulphate limited at entering concentrations of sulphate <300 μM. Neither the maximum specific growth rate (measured atDc) nor the observed molar growth yield for succinate decreased under sulphate limitation. The NADH oxidase in electron transport particles prepared from sulphate-limited cells was completely inhibited by PA. The stoichiometry of proton translocation associated with malate oxidation was similarly unaffected by sulphate limitation. It is concluded that (a) the respiratory chain of aerobic, heterotrophically grownPc.denitrificanspossesses three sites of energy conservation, including site III, (b) the number of protons ejected during the transfer of one pair of reducing equivalents along a region of the electron transport chain equivalent to a single energy-coupling site is 3, and (c) that sulphate limitation does not lead to a loss of proton translocation associated with the cytochrome-independent region of the respiratory chain.

ISSN:0008-4018    

DOI:10.1139/o78-003

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Since glutamine enters rat kidney mitochondria without exchange for an anion, the exit of its carbon skeleton must involve the dicarboxylate anion transporter (malate – inorganic phosphate) for ammoniagenesis to proceed. Therefore, this important mitochondrial anion transporter was studied in isolated renal cortex mitochondria. The phosphate concentration required for half-maximal rates of malate exit from renal cortex mitochondria of normal rats was 1.0 mM. This value was not decreased in renal cortex mitochondria from rats with chronic metabolic acidosis. The maximum velocity of the dicarboxylate transporter was not increased in renal cortex mitochondria from these acidotic rats. These kinetic parameters were similar in liver mitochondria. There was no acute activation of the dicarboxylate carrier when the incubation medium pH was lowered. Thus, there is no demonstrable activation of the dicarboxylate anion transporter in kidney cortex mitochondria of the rat with chronic metabolic acidosis. The significance of these results with respect to the regulation of renal ammoniagenesis is discussed.

ISSN:0008-4018    

DOI:10.1139/o78-004

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The nature of the cell surface constituent(s) containing sialic acid that block fixation of bacterial glycolipid mR595 to normal rat fibroblasts was explored. Indirect evidence suggests that a trypsin-sensitive, high molecular weight glycoprotein, present in larger amounts on the surface of normal cells (as compared with transformed rat fibroblasts), may be involved as a blocking agent.

ISSN:0008-4018    

DOI:10.1139/o78-005

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The use ofN-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) for coupling acyl-L-amino acids with aniline andp-nitroaniline has been investigated. Optically pure anilides are obtained in good yield but partial racemization occurred in one case.p-Nitroanilides cannot be obtained under similar conditions but if the reaction solvent is removed and the residue left for several days, coupling occurs giving a racemic product in moderate yields. Reaction mechanisms are proposed on the basis of isolated and characterized intermediates. It has been found thatN-benzoylamino acid anilides andp-nitroanilides are cleaved within a few minutes by hydrogen bromide in acetic acid to give theN-benzoylamino acid and the amine.

ISSN:0008-4018    

DOI:10.1139/o78-006

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

A purification method for an extracellular β-xylosidase (β-D-xyloside xylohydrolase, EC 3.2.1.37) induced inPenicillium wortmanniis described. It includes diafiltration, acetone precipitation, and hydroxylapatite chromatography. The enzyme has a molecular weight of about 100 000. Its pH optimum is at pH 3.3–4.0 and it is most stable at pH 5.0–6.0. Its isoelectric point is at pH 5.0. Sulfhydryl and histidine reagents are not inhibitory. The influence of added cations and anions is negligible.N-Bromosuccinimide oxidation of two to three tryptophan residues per molecule entails rapid inactivation. Glycon-specificity studies indicate strict requirements at C-2, C-3, C-4, and C-5, although α-L-arabinopyranosides are substrates. As the enzyme seems to hydrolyse xylooligosaccharides endwise, with retention of configuration in the reaction product, the enzyme is a true glycosidase, probably operating by a double-inversion mechanism.

ISSN:0008-4018    

DOI:10.1139/o78-007

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

By use of reverse phase 5 chromatography, a strain ofSaccharomyces cerevisiae(XB109-5B) has been shown to exhibit multiple isoaccepting forms for several of the transfer ribonucleic acids (tRNAs). This is in contrast with a standard wild-type strain where only one acceptor is found for each tRNA studied. Multiple peaks for tRNATyr, tRNAPhe, tRNASer, and tRNAValhave been detected for strain XB109-5B. However, the observation of multiple isoacceptors cannot be extended to all tRNAs in this strain since tRNAAspappears as a single form that is the same as in the wild type. The appearance of multiple peaks was found to depend on the growth conditions of the cells. The tRNA profiles of XB109-5B that was grown rapidly with vigorous aeration differed the most from profiles of comparably grown wild-type yeast, whereas tRNA from this mutant, grown without shaking or supplementary aeration, appeared the same as the wild type. The minor nucleoside composition of the isoacceptors of tRNAPhewas obtained.

ISSN:0008-4018    

DOI:10.1139/o78-008

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Rainbow trout cell cultures have been exposed to32P-labelled inorganic phosphate and the labelled RNA has been isolated. The 5S ribosomal ribonucleic acid (5S rRNA) was purified by polyacrylamide gel electrophoresis, then digested with RNase T1or pancreatic RNase. The products of complete digestion were separated and their sequences determined. These analyses have allowed a sequence to be proposed which differs in eight positions from that of mammalian 5S rRNAs.

ISSN:0008-4018    

DOI:10.1139/o78-009

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Aminopeptidase I activity which was found to be localized in the same subcellular fraction and to be similarly heat stable was partially purified by a common procedure fromEscherichia coliB,Escherichia coliK12,Enterobacter aerogenes,Salmonella typhimurium,Serratia marcescans,Pseudomonas aeruginosa, andProteus vulgaris. The enzyme preparations were shown to contain a single aminopeptidase active toward both leucylleucine and methionylalanylserine by mixed-substrate initial-velocity kinetic analysis. TheKmvalue for leucylleucine was virtually identical for the aminopeptidases of all of the organisms, as was theKmvalue for methionylalanylserine.

ISSN:0008-4018    

DOI:10.1139/o78-010

出版商:NRC Research Press    

年代:1978

数据来源: NRC