title: The ionic requirements for regulation by molluscan thin filaments.
abstract: Initial studies on molluscan muscle regulation indicated that thin filaments do not confer Ca2+-dependence on vertebrate myosin ATPase, and hence that molluscan muscles do not possess thin filament-linked regulatory systems. Subsequently it was shown that molluscan thin filaments do, in fact, impart Ca2+-sensitivity but only at Mg2+ concentrations greater than those used in the earlier studies. In the present study it is shown that Mg2+ prevents significant dissociation of tropomyosin and troponin subunits from thin filaments at the low monovalent ion concentrations typically employed to assay actomyosin ATPase; as a result Mg2+ allows expression of the molluscan thin filament regulatory system under these conditions.
mesh_terms: D000251:Adenosine Triphosphatases / Q000302:isolation & purification; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000502:physiology*; D008274:Magnesium / Q000502:physiology*; D008974:Mollusca / Q000378:metabolism*; D009124:Muscle Proteins / Q000378:metabolism*; D009132:Muscles / Q000201:enzymology / Q000378:metabolism*; D010125:Ostreidae; D011485:Protein Binding; D011817:Rabbits; D014335:Tropomyosin / Q000378:metabolism*; D014336:Troponin / Q000378:metabolism*
chemical_list: D009124:Muscle Proteins; D014335:Tropomyosin; D014336:Troponin; D000251:Adenosine Triphosphatases; D008274:Magnesium; D002118:Calcium