Activation of Inactive Phosphorylase Dimer and Monomer from Human Platelets with Magnesium Adenosine Triphosphate

Abstract

Abstract In human platelets, the activity of total phosphorylase could be increased appreciably following incubation with MgATP at 37° for 1 hour or overnight dialysis against MgATP at 4°. The total phosphorylase activity of a 4,000 x g homogenate increased 11-fold following MgATP activation. A 105,000 x g particulate fraction when assayed for phosphorylase activity in the presence of 1 mm AMP was inactive. Following treatment with MgATP at 37° for 1 hour, the fraction gained considerable activity. Sucrose gradient analysis of a 27,000 x g charcoal-treated platelet extract revealed the presence of inactive phosphorylase species with apparent molecular weights of dimer and monomer. These were converted to phosphorylase a as well as phosphorylase b following incubation with MgATP.