Contractile Proteins of a Benthic Fish. II. Composition and ATPase Properties of Actomyosin

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Abstract
SYNOPSIS. Actomyosin was extracted from skeletal muscle of Coryphaenoides, a benthic fish living at 2,200 meters depth, at a temperature of 2°C, or less, and at pressure of 3,000 psi. On SDS-urea electrophoresis on acrylamide gel, the actomyosin extracts yield components of apparent molecular weight 210,000 (myosin heavy chains), 47,000 (actin), 35,000 (tropomyosin and/or troponin subunits), and 13,000 (myosin light chains). The Mg2+-ATPase of Coryphaenoides actomyosin shows a complex Arrhenius plot, with marked denaturation at temperatures above 30°C, and diminished temperature sensitivity at temperatures below 15°C. Mg2+-ATPase is inhibited by pressure, with activation volumes of + 160 cc/mole at 25°C, and + 230 cc/mole at 2°C. Ca2+-ATPase of actomyosin exhibits the same pH, temperature, and pressure dependence as Ca2+-ATPase of myosin. The overall data would be consistent with a positive activation volume that is independent of temperature (to first approximation) and is related to the interaction of actin and myosin, and a negative activation volume that is temperature dependent and is related directly to activation of myosin ATPase. The net effect appears to be an adaptive mechanism whereby Mg2+-ATPase of Coryphaenoides actomyosin is relatively insensitive to pressure and temperature under conditions encountered by the living fish.

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