N-ethylmaleimide-modified heavy meromyosin. A probe for actomyosin interactions.

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Abstract
Treatment of rabbit skeletal muscle heavy meromyosin (HMM) with the sulfhydryl reagent N-ethylmaleimide (NEM) produces a species of HMM which remains tightly bound to actin in the presence of MgATP. NEM-HMM forms characteristic arrowhead complexes with actin which persist despite rinses with MgATP. NEM-HMM inhibits the actin activation of native HMM-ATPase activity, the superprecipitation of actomyosin, the contraction of glycerinated muscle myofibrils and the contraction of cytoplasmic strands of the soil amoeba Chaos carolinensis. NEM-HMM does not interfere with in vitro microtubule polymerization or beating of demembranated cilia.