Ordered phosphorylation of a duplicated minimal recognition motif for cAMP‐dependent protein kinase present in cardiac troponin I

Abstract

Cardiac troponin I contains two adjacent serines in sequence after three arginine residues thus making up a minimally duplicated recognition motif for cAMP-dependent protein kinase. In a synthetic peptide, PVRRRSSANY, the two serine residues are phosphorylated sequentially with the intermediate formation of a monophosphorylated species according to the following reaction sequence: Peptide k ₁|→ Peptide-P k ₂|→ Peptide-P₂. The calculated rate constants are: k ₁ = 0.435 min⁻¹ and k ₂ = 0.034 min⁻¹. Sequence analyses of the monophosphopeptide and its tryptic fragments show that the predominant monophosphoform carries phosphate at the second serine.