title: Desensitization of substrate inhibition of acto-H-meromyosin ATPase by treatment of H-meromyosin with rho-chloromercuribenzoate. Relation between the extent of desensitization and the amount of bound rho-chloromercuribenzoate1.
abstract: H-Meromyosin (CMB leads to betaME-H-meromyosin) was prepared by tryptic digestion of myosin, which had been treated with CMB bound to H-meromyosin and the extent of desensitization of the substrate inhibition of acto-H-meromyosin ATPase [EC 3.6.1.3.] was investigated. Both the dissociation of acto-H-meromyosin induced by ATP and substrate inhibition decreased with increase in the amount of bound CMB to a minimum value at about 1 mole of CMB bound per mole of H-meromyosin. The substrate inhibition of acto-H-meromyosin ATPase was restored to the original level by complete removal of the bound CMB by further treatment of CMB leads to beta ME-H-meromyosin with a large excess of beta-mercaptoethanol. The dissociation constant of acto-H-meromyosin in the presence of ATP decreased markedly on modification with CMB, while the maximum ATPase activity ar a sufficiently high concentration of F-actin remained essentially unchanged. Acto-H-meromyosin was reconstituted from F-actin and CMB LEADS TO beta ME-H-meromyosin, containing less than the stoichiometric amount of bound CMB. Its ATPase activity and the extent of dissociation of acto-H-meromyosin induced by ATP were explained as those of a mixture of unmodified H-meromyosin and CMB leads to beta ME-H-meromyosin containing 1 mole of CMB per mole of H-meromyosin. Half of the light chains (g2), with a molecular weight of 18,000, were removed from myosin by treatment with CMB and beta-mercaptoethanol. After this treatment, on further incubation of the myosin with a large excess of beta-mercaptoethanol, the myosin contained only half of the g2, but the substrate inhibition of acto-H-meromyosin ATPase was restored completely. The initial burst of P1 liberation and the EDTA-ATPase activity decreased to almost zero on specific modification of the SH1-groups with NEM, while the initial burst decreased to some extent and the EDTA-ATPase activity to 50% of the original value on binding of 1 mole CMB per mole of H-meromyosin. The actomyosin-type of ATPase activity was strongly inhibited by modification with CMB. The extent of the dissociation of acto-H-meromyosin induced by ATP was unaffected by modification with NEM, while it decreased on further treatment of NEM-myosin with CMB FOLLOWED BY BETA-MERCAPTOETHANOL.
mesh_terms: D000199:Actins; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002729:Chloromercuribenzoates / Q000378:metabolism / Q000494:pharmacology*; D004492:Edetic Acid / Q000494:pharmacology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008623:Mercaptoethanol / Q000494:pharmacology; D008970:Molecular Weight; D009132:Muscles / Q000032:analysis; D015879:Myosin Subfragments / Q000378:metabolism*; D009218:Myosins / Q000032:analysis; D011817:Rabbits; D013438:Sulfhydryl Compounds / Q000494:pharmacology; D014357:Trypsin / Q000494:pharmacology; D014361:Trypsin Inhibitors / Q000494:pharmacology
chemical_list: D000199:Actins; D002729:Chloromercuribenzoates; D015879:Myosin Subfragments; D013438:Sulfhydryl Compounds; D014361:Trypsin Inhibitors; D008623:Mercaptoethanol; D000255:Adenosine Triphosphate; D004492:Edetic Acid; D014357:Trypsin; D000251:Adenosine Triphosphatases; D009218:Myosins; D008274:Magnesium