Proteinase Activity in Muscle Particles

Summary. A particle preparation from mouse skeletal muscle displayed proteinase activity, which was maximum at approximately pH 3. Haemoglobin, glohin and myoglobin were attacked; there was little or no activity towards serum albumin, cytochrome C, insulin, 'Azocoll', or mixed muscle sarcoplasmic proteins. Activity was stimulated by cysteine or dithiothreitol but was not affected by any metal ions tested. Activity was released from the particles by acid or alkaline buffers, hypertonic NaCl and Triton X-100, but not by distilled water or by repeated freezing and thawing. The greater part of the muscle proteinase activity was associated with the particles.