Comparisons of the Tryptophan Synthase Inactivating Enzymes with Proteinases from Yeast

Abstract

The partially purified tryptophan synthase inactivating enzymes I and II were compared with the earlier described proteinases A, B and C by studying their catalytic properties, their sensitivity against a serine proteinase inhibitor and their temperature stability. Tryptophan synthase inactivase activities of inactivase I and II coincided with hemoglobin hydrolyzing and azocoll hydrolyzing activities, respectively, on hydroxyapatite column chromatography. Inactivase and hemoglobin hydrolyzing activities of the inactivase I fraction were insensitive to the treatment with phenylmethylsulfonyl fluoride, whereas inactivase and azocoll hydrolyzing activities of the inactivase II fraction were almost completely inhibited by phenylmethylsulfonyl fluoride. The N‐acetyltyrosine ethyl ester (Ac‐Tyr‐OEt) hydrolyzing activity of an inactivase I fraction from an hydroxyapatite column could be separated from the inactivase activity by DEAE‐Sephadex column chromatography. Because of its esterolytic properties, the separated fraction corresponds to proteinase C. Inactivase and hemoglobin hydrolyzing activities of the inactivase I fraction were stable at pH 6.0 and 37°C, but unstable at pH 8.0 and 37°C, while inactivase and azocoll hydrolyzing activities of the inactivase II fraction were unstable even at pH 6.0 and 37°C. From these studies it is concluded that inactivase I is identical to proteinase A, inactivase II is identical or very similar to proteinase B and that proteinase C had no tryptophan synthase inactivase activity. Copyright © 1974, Wiley Blackwell. All rights reserved