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N-ethylmaleimide-modified heavy meromyosin. A probe for actomyosin interactions
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. However, NEM-HMM does not interfere with in vitro microtubule polymerization or beating of demembranated cilia.
Insights
Treatment with N-ethylmaleimide (NEM) modifies heavy meromyosin (HMM) to create a stable actin-HMM complex. This NEM-HMM inhibits muscle and amoeba contraction but not microtubule polymerization or ciliary beating.
Area of Science:
- Biochemistry
- Muscle Physiology
- Cytoskeletal Dynamics
Background:
- Heavy meromyosin (HMM) is a key component of the actomyosin contractile system.
- Understanding HMM-actin interactions is crucial for elucidating muscle contraction mechanisms.
Purpose of the Study:
- To investigate the effects of N-ethylmaleimide (NEM) on rabbit skeletal muscle HMM.
- To characterize the functional consequences of NEM modification on HMM-actin binding and ATPase activity.
Main Methods:
- Treatment of rabbit skeletal muscle HMM with the sulfhydryl reagent N-ethylmaleimide (NEM).
- Analysis of NEM-HMM binding to actin using electron microscopy (arrowhead complexes).
- Assays for actin-activated HMM-ATPase activity, actomyosin superprecipitation, and muscle/cytoplasmic strand contraction.
Main Results:
- NEM treatment yields HMM (NEM-HMM) that binds tightly to actin, forming stable arrowhead complexes resistant to MgATP.
- NEM-HMM inhibits actin activation of HMM-ATPase, actomyosin superprecipitation, and contraction of muscle myofibrils and amoeba cytoplasmic strands.
- NEM-HMM does not affect in vitro microtubule polymerization or demembranated cilia beating.
Conclusions:
- NEM modification of HMM disrupts its normal interaction with actin, leading to inhibition of contractile processes.
- The results highlight the specific role of the modified site in actin-HMM interactions essential for muscle and cytoplasmic motility.
- NEM-HMM serves as a valuable tool for studying the mechanics of actin-based motility, distinguishing it from microtubule-based processes.