1. 1. The limited proteolysis of rabbit skeletal muscle phosphorylase a and b was studied with subtilisin BPN' imobilised to Sepharose 4B. 2. 2. The activity of phosphorylase b is nearly resistant to subtilisin under the conditions (pH 7.0, 30°C) where phosphorylase a rapidly loses its activity. 3. 3. The pH profile of phosphorylase a and b digestion is different. 4. 4. Proteolytic fragments of mol. wt 70,000 and 30,000 generated from phosphorylase a, while mol. wt 80,000 and 70,000 generated 'from phosphorylase b can be detected by SDS gel electrophoresis. 5. 5. Addition of AMP to phosphorylase b favours a conformation similar to-but not identical withphosphorylase a as recognised by subtilisin action.
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