Biological activities of the peptides obtained by digestion of troponin C and calmodulin with thrombin

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Abstract
Troponin C and calmodulin were not digested by thrombin at a significant rate in the presence of Ca2+. In the presence of EGTA [ethylene glycol bis[2-aminoethyl ether]N,N''-tetraacetic acid], [rabbit muscle] troponin C was digested by thrombin to yield 3 peptides: TH1 (residues 1-120), TH3 (residues 1-100) and TH2 (residues 121-159). In the presence of EGTA [bovine brain] calmodulin was digested by thrombin giving 2 peptides, TM1 (residues 1-106) and TM2 (residues 107-148). The electrophoretic mobilities of peptides TH1 and TM1 were increased at pH 8.6 by Ca2+ both in the presence and absence of urea. The mobilities of peptides TH2 and TM2 were unaltered under these conditions. Peptides TH1, TH3 and TM1 formed complexes with troponin I on polyacrylamide gels at pH 8.6 in the presence of Ca2+. The phosphorylation of troponin I by cAMP-dependent protein kinase was significantly inhibited by peptides TH1 and TH3, and to a lesser extent by peptide TM1. The calmodulin peptide TM1 activated myosin L chain kinase when present in large molar excess. Peptide TM2 did not activate the enzyme.