Two Non-Identical Heads of Myosin Molecules

抄録

Four different preparations of skeletal subfragment-1, denoted in this report as S1(Aa), S1(Ab), Sl(Ba), and S1(Bb), and two different preparations of cardiacsubfragment-1, denoted as S1(A) and S1(B), were obtained as described in ourrecent report (J. Biochem. 97, 965, 1985).
(i) The four preparations were obtained from chicken breast myosin trinitro phenylated with 2, 4, 6-trinitrobenzene sulfonate in the absence of inorganic pyro phosphate (-PP₁), and they were all shown to be trinitrophenylated. Addition of PP₁ caused change in the absorption spectra of trinitrophenyl(TNP)-S1(Aa) and TNP-S1(Ba), but not in those of TNP-S1(Ab) and TNP-S1(Bb). (ii) The two preparations of S1 were obtained from cardiac myosin trinitrophenylated either in the absence (-) or presence (+) of PP₁. S1(B) was trinitrophenylated, whereas S1(A) was not. Specifically emphasized is the observation that the yield of cardiac S1(A) was practically equal to that of cardiac SI(B). On the basis of these results, we propose the hypothesis of “two iso-myosins with non-identical heads, ” whichis essentially a combination of the hypothesis of isoenzymes and that of non-identical heads.