スルメイカ外とう膜筋ミオシンのトリニトロフェニル化がそのＡＴＰａｓｅ活性とＣａ感受性に及ぼす影響

Abstract

Trinitrophenylation of squid mantle myosin by 2, 4, 6-trinitrobenzene sulfonate, like that of rabbit myosin, proceeded in two distinct steps; an earlier fast reaction was followed by a slower reaction. However, some differences between squid and rabbit myosins were also observed: (a) The reaction occurred more quickly with squid myosin than with rabbit myosin. (b) Regardless of whether the trinitrophenylation was conducted in the presence or absence of inorganic pyrophosphate (PPi), one mol of trinitrophenyl (TNP) groups bound to 2.4×105g of squid myosin in the earlier fast step. (c) The addition of PPi caused no alteration of the absorption spectrum of squid myosin trinitrophenylated in the presence or absence of PPi, whereas it did alter the rabbit myosin trinitrophenylated in the absence of PPi.In the enzymic activities of Ca-, EDTA-, and Mg-ATPases, squid and rabbit TNP-myosin were very similar. Especially the difference between myosin trinitropheynlated in the absence of of PPi and myosin trinitrophenylated in the presence of PPi became distinctively clear in the Mg-ATPase activity of either squid or rabbit myosin. The effect of trinitrophenylation on Ca-sensitivity of the Mg-ATPase activity of squid myosin was practically parallel to that of the enzymic activity of myosin.It is therefore suggested that squid myosin, like rabbit myosin, has the “reactive lysine residues” in the proximity of the ATPase active site.