A method for isolation of troponin T kinase (ATP-protein phosphotransferase, EC 2.7.1.37) from rabbit skeletal muscles in proposed. The method gives a 7000-10 000-fold purification and results in an enzyme with specific activity of 400-800-nmol x min-1 x mg-1 of protein. The molecular weight of tropin T kinase as determined by gel filtration exceeds 500 000. Electrophoresis in polyacrylamide gel in the presence of sodium dodecyl sulphate revealed that isolated preparations of the enzyme consisted of at least three distinct proteins with apparent mol.wt. of 50 000, 46 000 and 31 000. The enzyme phosphorylates isolated troponin T at a rate which exceeds the phosphorylation rates of casein, phosvitin, histones, phosphorylase b and protamine 5-30-fold. Within the whole troponin complex, only troponin T is phosphorylated by the enzyme. The enzyme phosphorylates only the N-terminal serine residue of troponin T, i.e. the site that is normally phosphorylated in the whole troponin complex isolated from rabbit skeletal muscles.

Rabbit muscle D-glyceraldehyde-3-phosphate dehydrogenase was shown to serve as a substrate for Ca*+/calmodulindependent protein kinase II with a K,,, of 0.33 PM and a V,,,,, of 2.63 pmol.min-i.rng-i at pH 7.5 and 30°C. In the absence of calmodulin, the V,,, was halved and K,,, unchanged. 0.99 mol of phosphate was incorporated per tetrameric molecule of D-glyceraldehyde-3-phosphate dehydrogenase under the experimental conditions employed.Phosphorylation; D-Glyceraldehyde-3-phosphate dehydrogenase; Ca2+/calmodulin-dependent protein kinase II

Protein kinase C catalyzes phosphorylation of the rat skeletal muscle AMP-deaminase in the presence of calcium ions and phosphatidylserine. At the same time, the catalytic subunit of CAMP-dependent protein kinase fails to phosphorylate AMP-deaminase. CaZ', phosphatidylserine-dependent phosphorylation decreases three-fold (from 0.6 to 0.2 mM) the K,,, value and does not affect V,.. Protein kinase C-induced phosphorylation of AMP-deaminase, besides ADP-ribosylation, is suggested to be involved in regulating the AMP-deaminasc activity in vivo.

Rabbit skeletal-muscle troponin T was phosphorylated by a standard preparation of phosphorylase kinase [Cohen (1973)

No abstract