Sites phosphorylated in bovine cardiac troponin T and I. Characterization by 31P-NMR spectroscopy and phosphorylation by protein kinases.
Bovine cardiac troponin isolated in a highly phosphorylated form shows four 31P-NMR signals [Beier, N., Jaquet, K., Schnackerz, K. & Heilmeyer, L.M.G. Jr (1988) Eur. J. Biochem. 176, 327-334]. Troponin I, which contains phosphate covalently linked to serine-23 and/or -24 [Swiderek, K., Jaquet, K., Meyer, H. E. & Heilmeyer, L. M. G. Jr (1988) Eur. J. Biochem. 176, 335-342], shows three resonances. Mg2(+)-saturation of holotroponin shifts these troponin I resonances to higher fields. Direct binding of Mg2+ to the phosphate groups can be excluded. Both these serine residues of troponin I, 23 and 24, are substrates for cAMP- and cGMP-dependent protein kinases as well as for protein kinase C. Isolated bovine cardiac troponin T contains 1.5 mol phosphoserine/mol protein, indicating that minimally two serine residues are phosphorylated. One phosphoserine residue is located at the N-terminus. An additional phosphoserine is located in the C-terminal cyanogen bromide fragment, CN4, which contains covalently bound phosphate. Protein kinase C phosphorylates serine-194, thus demonstrating exposure of this residue on the surface of holotoponin.
Swiderek
K
K
Abteilung für Biochemie Supramolekularer Systeme, Ruhr-Universität Bochum, Federal Republic of Germany.
Jaquet
K
K
Meyer
H E
HE
Schächtele
C
C
Hofmann
F
F
Heilmeyer
L M
LM
D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D003488:Cyanogen Bromide; D046911:Macromolecular Substances; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008969:Molecular Sequence Data; D009206:Myocardium / Q000378:metabolism*; D010446:Peptide Fragments / Q000302:isolation & purification; D010449:Peptide Mapping; D010748:Phosphopeptides / Q000302:isolation & purification; D010758:Phosphorus; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D014336:Troponin / Q000378:metabolism*; D019210:Troponin I; D020107:Troponin T
D046911:Macromolecular Substances; D010446:Peptide Fragments; D010748:Phosphopeptides; D014336:Troponin; D019210:Troponin I; D020107:Troponin T; D010758:Phosphorus; D011494:Protein Kinases; D003488:Cyanogen Bromide