The study demonstrates that actin-activated ATP hydrolysis by myosin fragments involves two competing mechanisms catalyzed by a single species of myosin, sensitive to KCl concentration.
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KCl modulates myosin ATP hydrolysis pathways in vitro; leaves open physiological relevance to cardiac contractility.
The soluble proteolytic fragments of myosin, heavy meromyosin and subfragment 1, were prepared with varying amounts of the proteases chymotrypsin and papain, respectively. The actin-activated ATP hydrolysis were examined with oxygen-18-labeled ATP. Each preparation of heavy meromyosin and subfragments 1 displayed two pathways of ATP hydrolysis, called respectively the high and low oxygen exchange mechanisms. The contributions of the two mechanisms were found to be sensitive to the potassium chloride concentration. With a fixed concentration of actin (300 microM), the contribution of the low-exchange mechanism decreased from a maximum of 90% of the ATP hydrolysis at 10 and 20 mM KCl to 12% at 180 mM KCl. The results suggested that the two mechanisms were competing reactions catalyzed by a single species of myosin.
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Ikeuchi et al. (1986) studied this question.
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