Oxygen-dependent inactivation of gramicidin S synthetase in Bacillus brevis

Abstract

Incorporation of L-[14C]ornithine into gramicidin S by crude, unfractionated lysozyme extracts of B. brevis ATCC 9999 represented the activity of the gramicidin synthetase complex. Frozen-thawed cells were the source of active extracts, but when cells were shaken in air at 37.degree. C, they rapidly lost activity in a 1st-order reaction with a half-life of 13 min. Protease inhibitors and inhibitors of energy metabolism had no effect on the inactivation process in frozen-thawed cells. Stabilization was achieved when the cells were shaken in N2 or He instead of air. The addition of dithiothreitol produced a moderate degree of stabilization. The L-ornithine- and D-phenylalanine-activating activities of the gramicidin S synthetase complex were lost during aeration of the cells. Crude cell-free extracts also lost activity when they were shaken in O2, but, in this case, inactivation was slower (half-life of 80 min). N2 also stabilized these cell-free extracts.