Studies on gramicidin S synthetase. Purification and properties of the light enzyme obtained from some mutants of Bacillus brevis.

The phenylalanine-activating and/or-racemizing enzyme, i.e., the light enzyme, of gramicidin S synthetase was purified to a homogenous state by D-phenylalanine-Sepharose 4B chromatography from a wild and some gramicidin S-lacking mutant strains of Bacillus brevis. The light enzyme obtained from a mutant strain E-1 could activate phenylalanine but not racemize it, and had no phenylalanine-dependent ATP-[14C]AMP exchange activity, whereas the same enzyme obtained from other mutants and the wild strain had all three activities. Furthermore, the light enzyme of the mutant E-1 could form only acid-labile enzyme-bound phenylalanine, while the same fraction of the wild strain carried half of the enzyme-bound phenylalanine as acid-labile adenylate and half as a acid-stable thioester. These results suggest that the thiol site of the light enzyme of mutant E-1 might be damaged.