SUMMARY: An alkali-soluble glucan from the cell walls of Saccharomyces cerevisiae NCYC 1109 has been hydrolysed with a purified endo-(1 →-3)-β-D-glucanase and an endo-(1 → 6)-β-D-glucanase from Bacillus circulans WL-12. The products of enzyme action include various oligosaccharide and polysaccharide fractions which have been separated by gel filtration and characterized, giving new information on the fine structure of the glucan. The isolated cell walls have also been subjected to enzymic hydrolysis. The results suggest that part of the cell-wall mannan is held in place by a glucan component.
SUMMARY: A new method has been developed for measuring peptide transport in aminoacid auxotrophs of Escherichia coli by following induction of β-galactosidase. Appearance of the enzyme was determined after addition of inducer and peptides to amino-acid starved bacteria. For a given number of lysine equivalents, the rate and the extent of enzyme synthesis were the same for lysine and lysyl peptides; similar results were found for glycine and glycyl peptides. Saturation constants for peptide transport were determined from the exogenous peptide concentration that gave half maximal rates of enzyme synthesis. The saturation constants, studies with mutants defective in peptide transport, and detection of competition between peptides for uptake, all endorsed earlier conclusions from growth tests about the structural specificities for peptide transport. The new method is quicker, more sensitive and more informative than growth tests.
SUMMARY: During growth of Escherichia coli strain SPA o in the presence of methionine, an intermediate accumulates in the medium. This intermediate reacts with 2,4-dinitro-phenylhydrazine, and can be degraded to ethylene either enzymically or photo-chemically, the latter being stimulated by the addition of a flavin. The pH optimum for the photochemical degradation of this intermediate and 2-keto-4-methylthio-butyric acid (KMBA) is pH 3 whereas the optimum for methional is pH 6. The enzyme which converts the intermediate to ethylene also converts KMBA to ethylene and has many of the properties of a peroxidase including inhibition by catalase, cyanide, azide and anaerobiosis. The enzyme which synthesizes the intermediate is not known but requires oxygen and pyridoxal phosphate. A pathway for ethylene biosynthesis is proposed in which methionine is converted to KMBA which can be degraded either by peroxidase or in a flavin-mediated photochemical reaction. Its relevance to the properties of other ethylene-producing bacteria and to the proposed pathway of ethylene release by higher plants is discussed.