title: Interaction of phosphorylase kinase with polymyxins.
abstract: Nonactivated rabbit skeletal muscle phosphorylase kinase is inhibited by the polymyxins A, B, D and E when assayed at pH 8.6. Polymyxin B is the most effective inhibitor, causing 50% inhibition at 0.3 mM. Following the effect of polymyxin B on the kinase activity toward troponin, no inhibition was observed. In contrast, polymyxin B was found to greatly stimulate the autophosphorylation of phosphorylase kinase. About 10 mol of phosphate per tetramer (alpha beta nu delta) were incorporated in presence of polymyxin B (full autophosphorylation). This incorporation was about 6-fold higher than that observed without polymyxin. The stimulation of autophosphorylation by polymyxin B was accompanied with enhancement of the rate of autoactivation at pH 6.8.
mesh_terms: D000818:Animals; D004789:Enzyme Activation / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D009132:Muscles / Q000201:enzymology; D010764:Phosphorylase Kinase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010766:Phosphorylation; D011112:Polymyxin B / Q000494:pharmacology*; D011113:Polymyxins / Q000494:pharmacology*; D011817:Rabbits
chemical_list: D011113:Polymyxins; D010764:Phosphorylase Kinase; D011112:Polymyxin B