Mechanism of action of ethylene glycol on myosin A, myosin B and heavy meromyosin

Abstract

Forty percent E.G. 3 3 In this work the following abbreviations have been used: E.G. = ethylene glycol; Me + = divalent metal; ATPase = adenosine triphosphatase; MyB = myosin B; PCMB = hydroxymercurobenzoate; μ m P/mg/min = micromoles of phosphate per mg of protein per minute; Me + = monovalent metal; ATP = adenosine triphosphate; MyA = myosin A; DNP = 2,4,-dinitrophenol; HMM = heavy meromyosin. strongly accelerated the ATPase activity of MyA, MyB and HMM in the presence of 0.5 m K +, Rb + and NH 4 +. 5–10 m m Ca ++ inhibited 75–80% of the E.G. activation. In the same concentration E.G. increased the V m of the K + activated MyA ATPase and the Q 10 without changing the order of magnitude of the K m (1 × 10 −3 moles/L). Five to ten m m Ca ++ depressed both the V m and K m of the E.G. activated enzyme. In the presence of 40 Vol % E.G. MyA ATPase showed one broad optimal activity range between pH 7.5 and 9.0. The same enzyme in the presence of E.G. but in the absence of Ca + became very sensitive to photooxidation and was inhibited by low concentrations of PCMB (<5 × 10 −5 m). In the presence of 5–10 m m Ca ++ not only the activating effect of E.G. was depressed but also the increased sensitivity to photooxidation was reversed to a great extent. E.G. most probably interacted with some hydrophobic regions of the MyA molecule 1 and certain histidine and/or SH groups of the active site became involved indirectly in the conformational change. The Ca + effect can be explained by assuming that this ion in a concentration sufficiently high to saturate the active site acted as a stabilizer against the indirect attack of E.G. Superprecipitation and ultracentrifugal experiments indicated that 20–40 Vol % E.G. also weakened the physical interaction between actin and myosin regardless of the presence or absence of Ca +.