| Abstract: | The interaction between phosphorylase kinase (EC 2.7.1.38), isolated from rabbit skeletal muscles, and the ATP analogs with the modified triphosphate fragment: adenosine-5'-chloromethane pyrophosphonate (1), adenosine-5'-chloroethyl phosphate (2), adenosine-5'-bromethane pyrophosphonate (3), adenosine-5'-bromoethane phosphonate (4), adenosine-5'-chloroacetylaminomethane phosphonate (5), adenosine-5'-chloroacetylaminomethane pyrophosphonate (6) and adenosine-5'-chloromethane phosphonate (7), was studied. The compounds 1, 2 and 3 irreversibly inhibit the enzyme activity. In the presence of ATP the rate of inactivation is decreased. The radioactive compounds 1, 2 and 3 are stoicheometrically incorporated into the beta- and gamma-subunits of phosphorylase kinase. A correlation is shown to exist between the degree of the beta-subunit modification by compound 1 and the enzyme inactivation. The compounds 4, 5 and 6 inhibit the enzyme reversibly: in the presence of ATP complete protection of the enzyme activity is observed. The compound 7 does not affect the kinase activity; however, it binds itself to the beta-subunit of the enzyme. The binding of analogs 1 and 7 to the beta-subunit occurs at different sites. The data obtained are indicative of the catalytic role of the beta-subunit of phosphorylase kinase. |
