- Volume 65, Issue 1, 1971
Volume 65, Issue 1, 1971
- Article
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- Biochemistry
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A Study of the Lipase Produced by Anaerovibrio lipolytica, a Rumen Bacterium
More LessSUMMARY: Anaerovibrio lipolytica strain 5s, an anaerobic rumen bacterium, produced an extracellular lipase during exponential growth in batch cultures. The lipolytic activity was excluded from Sephadex G-200, and the purest preparations obtained contained two components when examined by electrophoresis or by ultracentrifugation and a large proportion of nucleic acid. The enzyme was most active at pH 7.4 and at 20 to 22°; activity was enhanced by Cal2 or BaCl2 while ZnCl2 and HgCl2 were inhibitory. Sodium chloride at high concentration was also inhibitory. Trilaurin was most rapidly hydrolysed of the triglycerides but diglycerides were more rapidly hydrolysed than were triglycerides.
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- Genetics And Molecular Biology
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Biochemical and Physiological Properties of Methionyl-sRNA Synthetase Mutants of Salmonella typhimurium
More LessSUMMARY: Two methionine auxotrophs (metG) of Salmonella typhimurium with the structural genes of the regulon intact have been studied. They possessed abnormal growth kinetics and the effect of the metG mutation on protein, ribonucleic acid and DNA synthesis suggested that these strains were impaired in their ability to synthesize protein; since they were able to synthesize methionine, but still required it for growth, they might have been defective in methionine activation for protein synthesis. To test this, this activity of methionyl-sRNA synthetase (L-methionine: sRNA ligase (AMP) EC 6.I.I.10) was determined in enzymic extracts of wild-type and metG strains. By using an acylation reaction the activation of methionine for protein synthesis was shown to be very decreased in metG extracts and this was reflect- ed in vivo by a decreased level of charged methionyl-sRNA in mutant bacteria; in the pyrophosphate exchange assay mutants showed greatly increased Km (methionine) values. The release of [3H]methionine from [3H]methionyl-sRNA was catalysed by wild-type extract, provided that pyrophosphate was present in the assay mixture, but not by the mutant extract. These results are discussed in relation to the two-part reaction catalysed by methionyl-sRNA synthetase. Mutant and wild-type enzyme behaviour differed at different pH values but not when subjected to chromatography on DEAE-cellulose or gel-filtration on Sephadex-G200. MetG mutants grown with limiting methionine had decreased values of all the biosynthetic enzymes except cystathionase, which was apparently de-repressed, suggesting that methionyl-sRNA was not the co-repressor for the methionine biosynthetic pathway.
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A Structural Gene for Neurospora crassa Isocitrate Lyase
More LessSUMMARY: A purification procedure for Neurospora crassa isocitrate lyase (ICL) is described. Thirteen mutants at the acu-3 locus produced no detectable ICL activity either on sucrose as sole carbon source or in the presence of acetate. These mutants also produced little or no protein able to neutralize anti-ICL antibodies. Selection of revertants, able to grow on acetate as sole carbon source, from one of the acu-3 mutants gave one class with moderately thermolabile and one with highly thermolabile ICL as well as apparently true revertants with ICL of wild-type stability. The mutants with highly labile ICL grew on acetate at 25° but not at 37°. One of the temperature-sensitive revertants was analysed genetically and shown to be due to further mutation within or close to acu-3 itself.
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- Medical Microbiology
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The Relationship between M-antigen and Opacity Factor in Group A Streptococci
More LessSUMMARY: M-protein and the opacity factor (OF) were both extracted by Lancefield's method from certain types of group A streptococci. The two proteins could not be separated by fractional precipitation with ammonium sulphate, column chromatography or polyacrylamide gel electrophoresis. The OF appeared to be closely associated with the high molecular weight fraction of the M-antigen, and there is some evidence that the two may form part of the same molecule.
M-protein and the OF were sought in various other extracts and preparations of M-positive and M-negative variants of serotypes which gave a positive serum opacity reaction (SOR). In all preparations from M-positive variants, the two proteins were always present. In M-negative variants, the OF present in the wall-membrane fraction could be extracted only by ‘phage-associated.’ lysin. All other extracts from M-negative variants were SOR-negative and M-negative. In the SOR-positive extract obtained by phage lysin treatment of M-negative variants, no M-antigen could be detected by precipitin tests, though the extracts contained a protein of similar electrophoretic mobility to the precipitin-positive protein in the extracts of the M-positive variants of the same serotype.
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- Physiology And Growth
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Unbalanced Growth in a Semi-continuous Culture System Designed for the Synchronization of Cell Division
More LessSUMMARY: Synchronization of division of Escherichia coli was induced in a semi-continuous culture system. A small-scale apparatus designed for the automatic operation of the system is described. The carbon (glucose)-limited defined medium was supplied at intervals of 1 to 4 h. and half of the diluted culture was discharged. After a number of cycles the glucose supplied each time was just sufficient for the doubling of the ‘self-established’ population. A logarithmic loss of viability occurred at the beginning of each cycle in the presence of fresh medium, and it was thought that part of the population underwent unbalanced growth. This phenomenon and the observation that the viable population consisted of two equal parts dividing synchronously but at different times were thought to reflect a post-division unequal competence of the emerging two halves of the population to cope with the active growth induced by the incoming fresh medium.
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Synthesis of Macromolecules and Polyribosome Formation in Early Stages of Spore Germination in Fusarium solani
More LessSUMMARY: Net synthesis of protein and RNA in germinating macroconidia of Fusarium solani began at the time of appearance of germ tubes, RNA being formed first; net DNA synthesis began much later. Studies on precursor incorporation indicated that the ungerminated spore, at the time of its removal from the parent mycelium, had a low but real capacity to synthesize both RNA and protein. Leucine incorporation rose very rapidly to a maximum at about 40 min. after harvest; even in the time required for conventional washing and filtration, incorporation capacity increased threefold. Ultra-centrifuge profiles showed polysome peaks after 15 min. incubation; evidence from ribonuclease treatment was consistent with the existence of polysomes in the spore at the time of removal from the mycelium. Neither protein nor RNA synthesis required a complete medium, but DNA was synthesized only in a medium that supported germination.
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Regulation of Isocitrate Dehydrogenase Activity in Escherichia coli on Adaptation to Acetate
More LessSUMMARY: Escherichia coli grown aerobically in glucose + salts medium excretes acetate. On glucose exhaustion, the cells synthesize the enzymes of the glyoxylate bypass which permits growth on acetate as sole source of carbon and energy. Concurrently, the activity of isocitrate dehydrogenase falls to 20% and, when the acetate is exhausted, is restored to 75% of the original level. Similar results are obtained after growth on substrates (e.g. glycerol) which do not promote excretion of acetate, provided acetate is added to the medium at the end of growth. This control of isocitrate dehydrogenase activity is apparently a mechanism which restricts the flow of carbon round the tricarboxylic acid cycle and favours operation of the glyoxylate bypass.
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- Short Communications
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