Comparisons of the Tryptophan Synthase Inactivating Enzymes with Proteinases from Yeast

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.1 Tryptophan synthase inactivase activities of inactivase I and II coincided with hemoglobin hydrolyzing and azocoll hydrolyzing activities, respectively, on hydroxyapatite column chromatography. 2 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. 3 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. 4 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.