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

Myosin was purified from the membrane fraction and the cytoplasm of human platelets, and the K+(EDTA)- and Ca2+-dependent ATPase activities were studied under various experimental conditions. The ATPase activity of the myosin from the membrane fraction was slightly lower than that of its cytoplasmic counterpart, regardless of the different assay conditions (pH, ionic strength, and temperature). Both myosins showed the same pH optima and a similar ionic strength dependence for the two ATPase activities measured. In addition, they exhibited the same substrate specificity using ATP, CTP, and GTP as substrates. The activation energy of the Ca2+-dependent ATPase activity was essentially the same for the two myosins, while the activation energy of the K+(EDTA)-dependent ATPase activity of the membrane myosin was higher than that of the cytoplasmic myosin. The ATPase activity of the membrane myosin was found to be more sensitive to freezing and thawing than the cytoplasmic myosin. The alkylation of the thiol groups by N-ethylmaleimide or N-iodoacetyl-N-(5-sulfo-1-naphtyl)ethylenediamine, and the trinitrophenylation of the lysyl residues by 2,4,6-trinitrobenzenesulfonate caused a significant decrease in the K+(EDTA)-dependent ATPase activity of the two myosins. However, the membrane myosin was much less affected than the cytoplasmic myosin. Actin induced inhibition of the K+ (EDTA) ATPase of both myosins, and much smaller quantities of actin were needed to inhibit the cytoplasmic myosin ATPase compared to quantities needed to inhibit the myosin ATPase from the membrane fraction. This indicates that the membrane myosin has a lower affinity toward actin. The observed variations in the ATPase activity of the myosins isolated from the membrane and the cytoplasm fractions of human platelets may reflect differences in their respective physiological functions.
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PMID:Characterization of the ATPase activities of myosins isolated from the membrane and the cytoplasmic fractions of human platelets. 614 26

The noncovalent fluorescent probe 6-propionyl-2-(dimethylamino)naphthalene (prodan) binds stoichiometrically to myosin subfragment-1 (S-1) without affecting the ATPase and actin-binding properties of S-1. Neither ATP nor actin interferes with the prodan binding. Free prodan exhibits a green emission peak at 520 nm. However, the prodan bound to S-1 and the S-1.ADP complex shows blue emission peaks at 460 and 450 nm, respectively, which allow easy separation of the fluorescence contributions from the free and bound probes. In the S-1.ADP.Pi state, the blue emission peak is further shifted to 445 nm with a large (4.5-fold) fluorescence enhancement. Thus, prodan in the presence of S-1 exhibits predominantly blue fluorescence only during ATP hydrolysis, and so visualizes the ATPase reaction continuously. The initial velocities of the steady state of the Mg2+-, Ca2+-, and actin-activated ATPases can be conveniently calculated from the blue fluorescence changes. The ability of different nucleoside triphosphates (NTP) to enhance the blue fluorescence of prodan follows the order ATP > CTP > UTP > ITP > GTP. This order agrees with those of the extent of hydrophobicity near the ribose of the corresponding nucleoside diphosphates (NDP) trapped to S-1 with orthovanadate (Vi) [Hiratsuka, T. (1984) J. Biochem. (Tokyo) 96, 155-162] and the ability of different NTPs to support force production in muscle fibers [Regnier, M., et al. (1993) Biophys. J. 64, A250]. The rate of formation of the corresponding S-1.NDP.Vi complex also follows this order, whereas the NTPase rate follows the reverse order. These results indicate that nucleotide-induced changes in prodan fluorescence correspond to the nucleotide-induced conformational states of S-1. Thus, the use of prodan in studies of the myosin ATPase offers a new and promising approach not only to monitoring the ATPase reaction but also to investigating the structural changes during ATP hydrolysis.
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PMID:Prodan fluorescence reflects differences in nucleotide-induced conformational states in the myosin head and allows continuous visualization of the ATPase reactions. 958 28