Cardiac troponin I, isolated from‐bovine heart, contains two adjacent phosphoserines

Abstract

Bovine cardiac troponin containing approximately 3 mol P/mol protein could be separated into its subunits without loss of phosphate. Troponin I and troponin T each contain about 1.5 mol P/mol protein. In troponin I two phosphorylated serine residues could be localized in the N‐terminal region by conversion of phosphoserine to S‐ethylcysteine. They are located in adjacent positions in the following sequence:‐Arg‐Arg‐Ser(P)‐Ser(P)‐Ala‐Asn‐Tyr‐Tyr‐Arg‐Ala‐Tyr‐Ala‐Thr‐Glu‐Pro‐His‐Ala‐Lys. This sequence shows that the first phosphoserine residue in bovine cardiac troponin I occupies a homologous position to phosphoserine‐20 of rabbit cardiac troponin I.