Covalent binding of ox heart myosin subfragment 1 to a cellulose matrix alters its ion specificity, making it activated by both Ca2+ and Mg2+, which resembles the enzymic action of the actin-subfragment 1 complex.
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May model actin-like myosin activation in vitro; leaves open relevance to intact cardiac myofibrils.
The preparation of ox heart myosin and its partial digestion with cellulose-bound papain is described. A procedure is outlined by which heavy meromyosin subfragment 1 can be covalently bound to a cellulose ion-exchange matrix. Attachment of heavy meromyosin subfragment 1 to the insoluble matrix results in a change in the ion specificity towards ATP hydrolysis. Unlike the soluble enzyme the bound form is activated by both Ca(2+) and Mg(2+). Maximal activation by Ca(2+) occurred at a lower concentration for the bound enzyme. Mg(2+) activates at a concentration which causes near-maximal inhibition of the Ca(2+)-activated adenosine triphosphatase (ATPase) of the non-bound enzyme. The Mg(2+)-activated ATPase of the bound enzyme was in turn inhibited by the presence of Ca(2+). The activation by Mg(2+) resembles the characteristic enzymic action of the actin-subfragment 1 complex.
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Liu-Osheroff et al. (1972) studied this question.
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