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At least 325 records · Page 18Linked to original sources
PubMed1974

Mechanism of action and development of resistance to a new amidino penicillin.

The mechanism of killing of Escherichia coli by a novel beta-lactam antibiotic, an amidino penicillin, has been investigated. This compound converts E. coli to relatively stable spherical forms at low concentration. However, the amidino penicillin caused no alteration in any of those parameters of peptidoglycan synthesis which can be studied. Above 10 mug of the antibiotic per ml the cells began to lyse, and a second mode of killing appeared. Mutants resistant to the amidino penicillin were isolated and several were studied in detail. Three mutant phenotypes were distinguished: (i) spherical shape and hypersensitive to lysis by either amidino penicillin or ampicillin; (ii) spherical shape and normally sensitive to lysis; (iii) rod shape, converted to viable spheres by amidino penicillin and normally sensitive to lysis.

Amidines↗
PubMed1973

Streptomyces DD-carboxypeptidases as transpeptidases. The specificity for amino compounds acting as carboxyl acceptors.

The ability of the water-soluble dd-carboxypeptidases of Streptomyces strains albus G, R61, K11 and R39 to perform transpeptidation was studied. The donor was diacetyl-l-lysyl-d-alanyl-d-alanine, and a whole range of amino acids, peptides and structurally related amino compounds were tested for acceptor function. No compound tested was an acceptor for the enzyme from strain albus G whereas the enzymes from strains R61 and K11 could utilize with varying efficiency a wide range of substances including peptides with N-terminal glycine or d-alanine, omega-amino acids, aminohexuronic acids, 6-aminopenicillanic acid and d-cycloserine. Certain peptides, when present in higher concentration, inhibited the transpeptidation observed at lower concentration. The enzyme from strain R39 would not use any dipeptide as an acceptor, but a few compounds that were not glycine or alpha-amino acids of the d-configuration did function thus. These were d-cycloserine and the lactams of meso- or racemic-diaminoadipic acid.

Carbon Isotopes↗
PubMed1973

Regulation of aspartokinase activity in Clostridium perfringens.

Cells of Clostridium perfringens type D apparently possess only a single species of aspartokinase. This enzyme has been partially purified and shown to be feedback inhibited by meso-diaminopimelate in an allosteric manner. The inhibitor exerts its action noncompetitively with respect to both substrates. The kinetic analysis further indicates that no homotropic cooperative interactions occur between either multiple substrate or inhibitor sites. Like aspartokinases from other bacteria, the clostridial enzyme is stimulated by the presence of either potassium or ammonium cations. A molecular weight of 102,000 was estimated for the enzyme following gel-filtration chromatography. Enzyme activity remains relatively constant throughout the growth cycle of the organism even well into the stationary growth phase. These results are discussed in terms of the role of the enzyme in the growth of the organism.

Aspartic Acid↗
PubMed1991

Peptides containing 2-aminopimelic acid. Synthesis and study of in vitro effects on bacterial cells.

Taking advantage of the peptide transport strategy, we have designed and synthesized several new peptides containing 2-aminopimelic acid (Apm), an inhibitor of the diaminopimelate pathway in bacteria: L-Lys-ambo-Apm, ambo-Apm-L-Lys, L-Lys-L-Ala-ambo-Apm, ambo-Apm-L-Ala-L-Lys, L-Ala(Cl)-ambo-Apm and ambo-Apm-L-Ala(Cl). In the two latter cases, Apm was associated with antibacterial amino acid beta-chloro-L-alanine [L-Ala(Cl)], an inhibitor of alanine racemase and transaminase B. The peptides displayed weak or no antibacterial activities; nevertheless, those containing L-Ala(Cl) had low MIC values in the presence of amino acids restoring protein synthesis. When tested on exponential phase Escherichia coli cells grown in minimal medium, the peptides were without effect or bacteriostatic, but important bacteriolytic effects could be observed, especially for the L-Ala(Cl)-containing peptides, when the growth medium was supplemented with specific amino acids. It was demonstrated that the weak or nil effect of the L-lysine-containing peptides was due to a poor uptake.

Amino Acid Sequence↗