title: Interaction of isozymes of myosin subfragment 1 with actin: effect of ionic strength and nucleotide.
abstract: Myosin subfragment 1 (S-1) can be fractionated into two isozymes, (A1)S-1 containing alkali light chain 1 and (A2)S-1 containing alkali light chain 2. The predominant difference in the behavior of the two isozymes of S-1 is that, at low ionic strength, the actin concentration required for half-maximal ATPase activity is considerably lower for (A1)S-1 than for (A2)S-1; that is, the apparent binding constant KATPase for (A1)S-1 is greater than KATPase for (A2)S-1 [Weeds, A.G., & Taylor, R.S. (1975) Nature (London) 257, 54-56]. This difference disappears at high ionic strength [Wagner, P. D., Slater, C. S., Pope, B., & Weeds, A.G. (1979) Eur. J. Biochem. 99, 385-394]. In the present study we investigated whether the difference in the KATPase values of (A1)S-1 and (A2)S-1 is due to a difference in the actual affinity of these S-1 isozymes for actin. Binding was measured in the presence of ATP and AMP-PNP and in the absence of nucleotide at varied ionic strengths. We found that at low ionic strength where KATPase is several times stronger for (A1)S-1 than for (A2)S-1, the binding of (A1)S-1 to actin is correspondingly stronger than that of (A2)S-1 irrespective of the nucleotide present. Furthermore, as the ionic strength is increased, just as the difference between the KATPase values for (A1)S-1 and (A2)S-1 disappears so too does the difference in the affinity of the two isozymes for actin.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000199:Actins / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000266:Adenylyl Imidodiphosphate / Q000494:pharmacology*; D000818:Animals; D004789:Enzyme Activation; D007527:Isoenzymes / Q000378:metabolism*; D007700:Kinetics; D009132:Muscles / Q000201:enzymology; D015879:Myosin Subfragments; D009218:Myosins / Q000378:metabolism*; D009994:Osmolar Concentration; D010446:Peptide Fragments / Q000378:metabolism*; D011485:Protein Binding; D011817:Rabbits
chemical_list: D000199:Actins; D007527:Isoenzymes; D015879:Myosin Subfragments; D010446:Peptide Fragments; D000266:Adenylyl Imidodiphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D009218:Myosins