The highly organized supramolecular structure of myofibrils profoundly affects the chemical properties and tryptic accessibility of the HMM/LMM hinge region of myosin.
Urges caution extrapolating isolated myosin findings to intact muscle; extends myofibril structural insights but leaves open in vivo cardiac relevance.
Limited proteolysis has been used to study the influence of actin, in the absence or presence of regulatory proteins of the thin filament (tropomyosin and troponin), as well as that of the myofibrillar structure on the tryptic cleavage of the heavy meromyosin (HMM)/light meromyosin (LMM) hinge region in myosin heavy chain. Cleavage at the HMM/LMM hinge is almost absent in myofibrils, whereas this hinge is accessible to tryptic digestion in actomyosin, in native thin filaments attached to myosin and in myosin heavy chain alone. This observation indicates that it is the myofibrillar structure which profoundly affects the tryptic accessibility of this specific hinge region of myosin. This provides a good example of the manner by which a highly organized supramolecular structure might affect the chemical properties of a specific site in a macromolecule.
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Assulin et al. (1986) studied this question.
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