Enzymatic properties of platelet actomyosin

The effects of various modifiers on the ATPase activity of bovine platelet actomyosin has been studied. The order of activation by monovalent cations was NH 4 + ⪢ K + > Li + > Na + . The order of activation by divalent cations was Ca 2+ > Mn 2+ = Sr 2+ > Ba 2+ > Co 2+ > Mg 2+ > Zn 2+ . Ethylenediaminetetraacetate inhibits. Activity increased with increasing concentrations of monovalent cations, except for inhibition by increasing concentrations of NH 4 + in the presence of Ca 2+ . Adenosine triphosphatase activity was increased by low concentrations of urea and trypsin, but was unaffected by low concentrations of N -ethylmaleimide. For all enzymatic properties where direct comparisons are possible, actomyosin from platelets is unlike that from skeletal muscle, but is similar to that from smooth muscle and non-muscle sources.