Essential arginine residue in gramicidin S synthetase 1 of Bacillus brevis

Phenylalanine activation of gramicidin S synthetase 1 (GS 1) [EC 5.1.1.11] of Bacillus brevis is inhibited by phenylglyoxal. The inactivation of GS 1 by phenylglyoxal obeys pseudo-first-order kinetics and formation of a reversible enzyme-reagent complex prior to modification is indicated. Both ATP and phenylalanine prevent the inactivation by phenylglyoxal. ATP is competitive with phenylglyoxal, whereas phenylalanine is not. In the presence of ATP, one residue of arginine per mol of protein is protected from the modification as determined by amino acid analysis and incorporation of [7-14C]phenylglyoxal. These results indicate that a single arginine residue of GS 1 is essential for phenylalanine activation in binding the phosphate moiety of ATP.

Characteristics of beta, beta-difluoroalanine and beta, beta, beta -trifluoroalanine as suicide substrates for Escherichia coli B alanine racemase

The alanine racemase from Escherichia coli B has been shown to process DL isomers of beta -fluoroalanine as suicide substrates with an identical partitioning ratio for each enantiomer of 820 catalytic eliminations of HF per enzymatic inactivation event [Wang, E., & Walsh, C. T. (1978) Biochemistry 17, 1313], suggesting the aminoacrylate--PLP complex as a common, symmetrical partitioning species. In an attempt to vary the partition ratio, an index of killing efficiency, systematically the beta, beta-difluoroalanine and beta, beta, beta-trifluoroalanine isomers have now been evaluated for substrate processing, suicidal inactivation kinetics and partitioning ratio, and stability of inactive, derivatized enzyme forms. Both difluoroalanine isomers show high Km values (116 mM for D, 102 mM for L) in catalytic HF loss to form fluoropyruvate. The Vmax for the D isomer is about 14-fold higher than that for the L isomer. Limiting inactivation rate constants, calculated from kcat and observed partition ratios of 5000 and 2600, respectively, are 2.2 min-1 for D-difluoroalanine and 0.33 min-1 for L-difluoroalanine. For comparison, DL-trifluoroalanine turns over less than 10 times per enzyme molecule inactivated and so is a very efficient suicide substrate. The estimated inactivation rate constant is less than or equal to 1.0 min-1. These data are analyzed in terms of partitioning behavior of the monofluoro- and difluoroaminoacrylate--PLP complexes as partitioning intermediates for turnover or for racemase inactivation. While mono- and trifluoroalanines yield stable inactive species, the difluoroalanine isomers produce labile enzyme derivatives, and regain of catalytic activity is analyzed in terms of the anticipated oxidation state at the beta carbon of the substrate fragment adducted to the enzyme.

Arginine regulation of gramicidin S biosynthesis

Several amino acids are known to affect the gramicidin S producer Bacillus brevis ATCC 9999 with respect ot growth, soluble gramicidin S synthetase formation, antibiotic production, or a combination of these. Our studies confirmed that arginine has paradoxical effects on the B. brevis fermentation; it markedly increased growth and antibiotic production, yet decreased the soluble heavy gramicidin S synthetase activity. We found that arginine did not repress heavy gramicidin S synthetase. The amino acid stimulated growth and increased specific antibiotic production presumably by supplying a limiting precursor (ornithine) for gramicidin S synthesis. Although the amino acid decreased the specific activity of the soluble heavy gramicidin S synthetase, it markedly increased the particulate enzyme activity which persisted hours after the soluble heavy gramicidin S synthetase disappeared. One percent arginine was the optimum level for growth and gramicidin S production. After growth in 1% arginine, heavy synthetase activity in the particulate fraction more than doubled. We propose that arginine leads to the soluble enzyme becoming membrane bound and more stable in vivo. Although we found arginine capable of inhibiting the action of soluble heavy gramicidin S synthetase, this was not the mechanism involved in the lowering of soluble heavy gramicidin S synthetase specific activity.

Inhibition of bacterial growth by beta-chloro-D-alanine

The D- and L-isomers of beta-chloroalanine inhibit the growth of Diplococcus pneumoniae, Streptococcus pyogenes, Bacillus subtilis, and Escherichia coli. With pneumococcus the inhibition by beta-chloro-D-alanine is completely prevented by either D-alanine or D-alanyl-D-alanine, while L-alanine is not effective in preventing the inhibition. The inhibition of growth by beta-chloro-L-alanine is not affected by D-alanine and is only partially prevented by high concentrations of L-alanine. The intracellular free alanine in untreated E. coli and B. subtilis is about 95% in the D-configuration while the free intracellular alanine in both organisms after treatment with beta-chloro-D-alanine is predominantly the L-isomer. These results suggested that the beta-chloroamino acid inactivates alanine racemase (EC 5.1.1.1). Indeed, when extracts of E. coli or B. subtilis were treated with beta-chloro-D-alanine, the activities of alanine racemase and of D-glutamate-D-alanine transaminase were found to be 90-95% inhibited. Studies with mice have shown that beta-chloro-D-alanine is an effective antibacterial agent in vivo againt D. pneumoniae, S. pyogenes, and E. coli.

D-alanine oxidase from Escherichia coli: participation in the oxidation of L-alanine

Cell wall-membrane preparations of Escherichia coli, prepared by the ethylenediaminetetraacetic acid-lysozyme method, contain enzymes which catalyze the oxidation of d-alanine and, to a lesser extent, l-alanine into pyruvate and ammonia without the formation of hydrogen peroxide. The kinetic parameters were (i) pH optima of 8.3 to 8.4 for l- and d-alanine and (ii) a K(m) value of 6.6 +/- 0.2 mM for d-alanine. Several coenzymes were without effect when added to the reaction mixture. The participation of d-alanine oxidase in the oxidation of l-alanine was demonstrated. The evidence is based on (i) results of cellular fractionation; (ii) labeling experiments; (iii) inhibition studies with aminooxyacetate and cycloserine; (iv) denaturation experiments; and (v) demonstration of the presence of an active racemase.