Studies on the Yeast Photoreactivating Enzyme

Large scale preparation of purified photoreactivating enzyme from commercial bakers' yeast has been described. The enzyme has been purified approximately 3000-fold over the crude extract with an over-all yield of 5 to 6%. The purified enzyme has a pH optimum at 7.2 and does not require any metal ions for activity. High phosphate concentration inhibits enzyme activity with an optimum activity at 0.02 m phosphate. The purified enzyme shows no absorption peaks between 300 and 400 mµ and has a small amount of typical cytochrome absorption. Analytical ultracentrifugation of the purified enzyme indicates the presence of one large homogeneous component and another small component which does not show a peak in the schlieren pattern, but absorbs light at 546 mµ. The average molecular weight of the large component is ∼30,000.