Gramicidin S-synthetase. Preparation of the multienzymic complex with a high specific activity.

A new purification procedure for the multienzyme of gramicidin S-synthetase has been developed. In vitro proteolysis with partial inactivation is suppressed by protease inhibitors EDTA, phenylmethylsulfonylfluoride, and fast preparation methods during initial separation steps. Activity has only been assayed by the total reaction of gramicidin S-synthetase, not by partial reactions of amino acid activation. The assay has been improved by evaluation of inhibitory concentrations of buffers, salts, and the product gramicidin S. It has been demonstrated that the rate of peptide synthesis in extracts containing both enzymes of gramicidin S-synthetase depends on protein concentration in a second order function. The multienzyme or heavy enzyme has been purified about 1400-fold to a specific activity of 24 nM/min per mg of protein, and the relation of this activity to the calculated in vivo activity is discussed.