Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.4.1 (myosin ATPase)
 1,140 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To test the possibility that ATP diffusion limits the kinetics of myosin ATPase (EC. 3.6.1.3) in situ, myosin was covalently bound to the surface of 2 kinds of films: collagen and Immunodyne. On collagen films, it was bound either with 1-ethyl-3 (3 dimethyl-aminopropyl)carbodiimide (EDC) or with dimethyl-3,3'-dithiobis(propionimidate) (DTP). The apparent Km for K+-ATP rose from 0.26 mM for free myosin in solution to 2-5 mM for covalently bound myosin, and maximum K+-ATPase activity was very low. With the other film, Immunodyne from Pall, the maximum activity of bound myosin was 170 nmol per min per 1.5 cm2 film. The apparent Km for K+-ATP was 2.1 mM when the incubation mixture was vigorously stirred, and the effect of stirring indicated that the kinetics of K+-ATP hydrolysis are limited by external diffusion. The large amount of myosin bound per unit of Immunodyne film surface permitted the study of Mg2+-ATPase activity, although it was 400-500 times less than the K+-ATPase activity. The apparently non-Michaelian kinetics of Mg2+-ATP hydrolysis are attributable to the external diffusion. The apparent Michaelis constant observed at low Mg2+-ATP concentrations rose from 0.27 microM for myosin in solution to 5 microM for myosin bound to Immunodyne film.
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PMID:Diffusion-limited kinetics of immobilized myosin ATPase. 252 82

The role of the rotational dynamics of actin filaments in their interaction with myosin was studied by comparing the effect of myosin subfragment 1 (S1) with two other structural perturbations, which have substantial inhibitory effects on activation of myosin ATPase and in vitro motility of F-actin: (1) binding of the antibody fragment Fab(1-7) against the first seven N-terminal residues and (2) copolymerization with monomers treated with the zero-length cross-linker 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDC), referred to as EDC-actin. The rotational motion of actin was measured by time-resolved phosphorescence anisotropy (TPA) of erythrosin iodoacetamide (ErIA) attached to Cys 374 on actin. The binding of S1 in a rigor complex (no nucleotide) induced intramonomer (allosteric) and intermonomer (cooperative) structural changes that increased the residual anisotropy of labeled F-actin, indicating a conformational change in the region of the C terminus. Similar allosteric and cooperative changes were induced by binding of Fab(1-7) and by copolymerization of the ErIA-labeled actin monomers with EDC-actin. This suggests that the functional perturbations transform actin to a form resembling the rigor actomyosin complex. The correlation of the perturbation-induced changes in TPA of actin with the functional effects suggests that the actomyosin interaction can be inhibited by stabilization of actin in one of its structural intermediates.
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PMID:Perturbations of functional interactions with myosin induce long-range allosteric and cooperative structural changes in actin. 933 42