A comparative study of crystallized silky and lemon shark muscle glycogen phosphorylases

1. 1. Silky and lemon shark muscle glycogen phosphorylases b and a were purified and crystallized under similar conditions. In contrast to other phosphorylases, both enzymes crystallize from ammonium sulphate or buffer. The doubling in molecular weight observed upon phosphorylation to the a form is similar to that of homoiothenns but different from that of other poikilotherms (frog and lobster). 2. 2. The enzymes from these a shark species are more stable than those from muscle of homoiotherms and, like lobster phosphorylase, they require no sulphydryl compounds for maintaining their activity. 3. 3. Lemon and silky shark phosphorylases appear to be immunologically identical and distinct from the phosphorylases of rabbit or human muscle. 4. 4. The fact that phosphorylase from lemon or silky shark can be prepared in homogenous form, crystallized, and stabilized in dilute buffer without need for the activator 5/-AMP, sulphydryl compounds, or a high concentration of salts, makes it unique among the glycogen phosphorylases and particularly useful for research purposes.