EFFECTS ON PROPERTIES OF A THIOL PROTEASE FROM XENOPUS EMBRYOS OF CHANGES IN SUBSTRATE AND ASSAY CONDITIONS

A protease was purified from Xenopus embryos. Proteolytic activity of the protease against BSA had an optimum pH of 3.8 in acetate buffer an d was not detectable at neutral pH. However, when embryonic proteins w ere used as substrates and digested in phosphate buffer, proteolysis o f embryonic proteins was enhanced and was detectable from pH 5.0 to pH 7.0. Digestion of three proteins were mainly detected in digestion of total embryonic proteins. The proteins digested had the same mobiliti es (on SDS polyacrylamide gel) as yolk proteins. The protease was pres ent in the cytoplasm and around yolk granules. We propose that this pr otease mainly cleaves a certain yolk proteins in the cytoplasm of Xeno pus embryos.