1. Of four proteolytic enzymes isolated from autolysing Saccharomyces carlsbergensis, one is inactivated at about 45°C, whereas the others are stable at 50°C. pH optima for activity are from 3.0 to 8.0 but maximum stability is between pH6.0 and 6.5. All appear to be glycoproteins, the carbohydrate moiety containing glucose and mannose residues. 2. Lysed protoplasts of the same yeast release four proteolytic enzymes each of which have two pH optima at pH3.0 and 7.0 approximately. Compared with the enzymes from autolysed yeast, resistance to high temperature is much less, and they are not glycoprotein in nature. 3. The same yeast grown with N-acetyltyrosine ethyl ester as nitrogen source secretes into the medium four proteases believed to be glycoprotein in nature. Generally they resemble the enzymes from lysed protoplasts more than those from autolysing yeast.
