Phosphorylase kinase phosphorylation of skeletal-muscle troponin T

Abstract

Rabbit skeletal-muscle troponin T was phosphorylated by a standard preparation of phosphorylase kinase and by fractions obtained after chromatography of phosphorylase kinase on phosphocellulose. The original preparation of phosphorylase kinase phosphorylated at least 2 sites, one of which was serine-1. The 2nd and probably the 3rd sites were presumably located in the peptide flanked by amino-acid residues 147 and 161 of troponin T. Fractions of phosphorylase kinase adsorbed on phosphocellulose phosphorylated only the 2nd site. Tightly adsorbed fractions possessed high troponin T kinase and phosvitin kinase activities and phosphorylated only serine-1 of troponin T. Standard preparations of phosphorylase kinase are contaminated by troponin T kinase, which can phosphorylate serine-1 of troponin T.