Protein kinase C phosphorylation of cardiac troponin I or troponin T inhibits Ca2(+)-stimulated actomyosin MgATPase activity

Effects of troponin phosphorylation on Ca2(+)-stimulated MgATPase activity of bovine cardiac actomyosin were examined. Phosphorylation by protein kinase C of troponin I and troponin T subunits in troponin or troponin-tropomyosin complex resulted in a decreased Ca2(+)-stimulated MgATPase activity in...

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Bibliographic Details
Published in:The Journal of biological chemistry 1991-03, Vol.266 (8), p.4974-4978
Main Authors: Noland, T A, Kuo, J F
Format: Article
Language:English
Subjects:
Actomyosin - metabolism
Analytical, structural and metabolic biochemistry
Animals
Biological and medical sciences
Ca(2+) Mg(2+)-ATPase - metabolism
Calcium - pharmacology
Cattle
Contractile proteins
Fundamental and applied biological sciences. Psychology
Holoproteins
Kinetics
Myocardium - metabolism
Phosphorylation
Protein Kinase C - metabolism
Proteins
Troponin - metabolism
Troponin I
Troponin T
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Summary:Effects of troponin phosphorylation on Ca2(+)-stimulated MgATPase activity of bovine cardiac actomyosin were examined. Phosphorylation by protein kinase C of troponin I and troponin T subunits in troponin or troponin-tropomyosin complex resulted in a decreased Ca2(+)-stimulated MgATPase activity in reconstituted actomyosin, and this effect was reversed by subsequent dephosphorylation by protein phosphatase 1. It was further observed that protein kinase C phosphorylation of either troponin I or troponin T subunits led to a similar inhibition of Ca2(+)-stimulated actomyosin MgATPase activity. In all cases, EC50 values (concentrations causing 50% stimulation) for Ca2+ were not appreciably affected by troponin phosphorylation by protein kinase C. Data from phosphorylation site analysis suggests that phosphorylation of threonine 144 in troponin I and possibly threonine 280 or threonine 199 in troponin T might be important for the observed decrease of Ca2(+)-stimulated actomyosin MgATPase. It is suggested that inhibition of actomyosin MgATPase caused by protein kinase C phosphorylation of troponin I and/or troponin T represents a new mechanism that can account for in part the reported negative inotropic effect of phorbol esters on various cardiac preparations.
ISSN:0021-9258
1083-351X
DOI:10.1016/S0021-9258(19)67744-6