Regulatory mechanism in smooth muscle: actin-linked regulation.
Our view about the Ca regulation of smooth muscle contraction can be summarized as follows: the regulatory system is actin-linked and consists of tropomyosin and leiotonin; the latter is a complex of two proteins, leiotonin A, the regulatory moiety, and leiotonin C, the Ca-binding moiety. Leiotonin resembles troponin in some respects, but is clearly different in that it has no affinity for tropomyosin and is effective at a leiotonin/actin molar ratio of less than 1:50. The methods of preparing leiotonin were critically reviewed and a suggestion was provided for the development of a new procedure. References were also made to our idea that the myosin light chain phosphorylation may not play an essential role in smooth muscle contraction. With reference to a new type of actin-linked factor from Physarum polycephalum through which Ca2+ represses the actin-myosin-ATP interaction, the diversity of the modes of action of Ca2+ was discussed.
D000199:Actins / Q000378:metabolism*; D000818:Animals; D001717:Birds; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D005895:Gizzard, Avian; D006801:Humans; D009119:Muscle Contraction; D009124:Muscle Proteins / Q000378:metabolism; D009130:Muscle, Smooth / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism; D013552:Swine; D014335:Tropomyosin / Q000378:metabolism; D014336:Troponin / Q000378:metabolism
D000199:Actins; D002147:Calmodulin; D009124:Muscle Proteins; D014335:Tropomyosin; D014336:Troponin; C018993:leiotonin; D011494:Protein Kinases; D002118:Calcium