Trinitrophenylation of the reactive lysine residue in double-headed myosin in the presence of PP.

Lys-83 in the heavy chain of rabbit skeletal muscle myosin is rapidly and stoichiometrically modified by trinitrobenzene sulfonate. Other authors claimed that the half-stoichiometric trinitrophenylation of Lys-83 in myosin in the presence of PPi was correlated to a Pro/Ser microheterogeneity at the 78th residue position in the heavy chain [Miyanishi, T., Maita, T., Matsuda, G., & Tonomura, Y. (1982) J. Biochem. 91, 1845-1853]. However, our recent studies with chymotryptic subfragment 1 (S1) instead of myosin showed no such correlation between the half-stoichiometric trinitrophenylation and the Pro/Ser microheterogeneity [Komatsu, H. & Tawada, K. (1993) J. Biol. Chem. 268, 16974-16978]. Since the global structure of the head portion of myosin is different from that of chymotryptic S1 that lacks DTNB light chain, it could be argued that the difference is due to the structural difference between chymotryptic S1 and myosin. We hence reexamined the situation with myosin, and obtained the same results as found with S1: (i) Lys-83 in myosin was half-stoichiometrically trinitrophenylated in the presence of PPi, although it was stoichiometrically modified in the absence of PPi; (ii) there was a Pro/Ser microheterogeneity at the 78th position in the myosin heavy chain, which was not correlated to the half-stoichiometric trinitrophenylation of Lys-83 in the presence of PPi.