Studies on Gramicidin S Synthetase

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Abstract
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 chro-matography from a wild and some gramicidin S-lacking mutant strains of Bacillus brevis. The light enzyme obtained from a mutant strain E-l 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-l 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 acid-stable thioester. These results suggest that the thiol site of the light enzyme of mutant E-l might be damaged.