Small sub-units of myosin

Several reports have recently appeared of low- molecular-weight components dissociated from rabbit skeletal myosin. Denaturation in 5M- guanidine hydrochloride gave a light component of mol.wt. 46000 (Dreizen, Hartshorne & Stracher, 1966), whereas treatment with 0-1M-Na2CO3 at pH 11 -0 produced a fraction of mol.wt. 20000 that gave three bands on cellulose acetate electro- phoresis (Gershman, Dreizen & Stracher, 1966). Acetylation (Locker & Hagyard, 1967b) or suc- cinylation (Oppenheimer, Barany, Hamoir & Fenton, 1967) also gave low-molecular-weight components. Some of these might, of course, be adsorbed impurities in the myosin preparations, but Locker & Hagyard (1967b) have shown that a fraction (AcMII) of mol.wt. about 20000 could be obtained in yields of up to 15% of the total material by DEAE-cellulose chromatography of the low- molecular-weight material from myosin purified by either (NH4)2SO4 fractionation (Kielley & Harrington, 1960) or DEAE-cellulose treatment (Takahashi, Hashimoto & Tonomura, 1963). Further, Locker & Hagyard (1967a) obtained low- molecular-weight material from myosin by car- bonate or tripolyphosphate treatment, or heat coagulation, that gave, after acetylation, the three electrophoretic components characteristic of frac- tion AcMII. The question arises whether these components are similar in amino acid sequence. I now describe some experiments that suggest that this may be so.