The site of phosphorylation of troponin I in the perfused rabbit heart. The effect of adrenaline

Abstract

On treatment of the perfused rabbit heart with adrenaline [epinephrine] the total covalently bound phosphate of troponin I increased from 1.14-1.86 mol of phosphate/mol. Covalently bound phosphate was identified only in the region of the molecule of cardiac troponin I consisting of residues 1-48. When 32P-labeled orthophosphate was present in the perfusion medium the phosphate at Ser-20 became radioactively labeled. This residue was the only significant site of phosphorylation that could be identified. The addition of adrenaline caused a 4- to 5-fold increase in covalently bound [32P]phosphate. Virtually all of the 32P was located at Ser-20. Apparently the extent of phosphorylation of Ser-20 of cardiac troponin I increased from 30-40% in the control perfused heart to about 100% in the presence of adrenaline.