[Properties of the catalytically active fragment obtained by limited proteolysis of phosphorylase kinase].

The activation of phosphorylase kinase by limited proteolysis with subtilisin results in a formation of new enzyme forms differing in their molecular weights. Using gradient electrophoresis in polyacrylamide gel, it was shown that the high molecular weight fraction is made up of active fragments having different molecular weights. The low molecular weight fraction was found to contain only one active fragment with molecular weight of 80 000. Disc electrophoresis in polyacrylamide gel demonstrated that the active fragments of the high and low molecular weight fractions are not homogenous. The kinetic properties of the low molecular weight fragment were investigated. It was found that at pH 8.2 the native non-activated kinase and the catalytically active fragment have identical Km values for the substrates (phosphorylase B and MgATP); however, unlike the non-activated kinase, this fragment possesses a decreased sensitivity to Ca2+ and effectors (glycogen and glucose 6-phosphate) and has no optimum of activity within the pH range of 6.0-9.0.