The Optical Rotatory Dispersion of Myosin A

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Abstract
The changes in the -b0 term of optical rotatory dispersion of myosin on addition of adenosine triphosphate (ATP), magnesium pyrophosphate (MgPP) and p-chloro-mercuribenzoate (PCMB) were re-examined under various conditions. The direction and magnitude of the change in the -b0 term (-5% to +5%) on the addition of ATP were dependent on the season of preparation of myosin. The -b0 term decreased mainly with myosin obtained in winter and early spring and increased with myosin obtained in other seasons. The two types of preparation had several roperties in common. Thus, the absolute value of the change in -b0 caused by ATP was maximal at pH 7.0 to 7.3, increased with decrease in temperature, and was depressed by removal of tightly bound Ca++ from myosin by treatment with PCMB and [beta]-mercaptoethanol. The change caused by ATP was also observed in NaCl and in the presence of EDTA. A decrease by several per cent in the -b0 term on addition of MgPP was observed with both types of myosin preparation, and was maximal at pH 7.0 to 7.3. An Increase in -b0 caused by 4 moles PCMB per 105 g. protein and a decrease in -b0 caused by 8 moles PCMB per 105 g. protein were observed with both types of myosin. The spectrophotometric titration curve of tyrosine in myosin, obtained by extrapolating the time-course of the change in optical density at 295 m[mu] to zero time, only showed an abnormality in the narrow range from pH 9.0 to 10.7, and was unchanged on addition of MgPP. However, the addition of MgPP decreased the amount and the rate of dissociation of those tyrosine residues which dissociate gradually at pH 10.5.