Dependence of in vivo inactivation kinetics of gramicidin S synthetase on cell physiology.

Gramicidin S synthetase, the enzyme complex catalyzing the biosynthesis of the antibiotic gramicidin S in Bacillus brevis, is subject to O(2)-dependent in vivo inactivation during exponential aerobic growth after reaching a peak in specific activity. The five amino acid substrates of the synthetase are capable of stabilizing its activity to varying degrees in whole cells shaken aerobically. Depending on the time of cell harvesting before, during, or after the peak in intracellular gramicidin S synthetase specific activity, the enzyme has a long, medium, or short half-life, respectively. The kinetic profiles of gramicidin S synthetase in B. brevis cells indicate that both the kinetics of synthetase loss and the degree of its amino-acid-mediated stabilization are a strong function of the cells' physiological development.