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

SYNOPSIS. Actomyosin was extracted from skeletal muscle of Coryphaenoides,a benthic fish living at 2,200 meters depth, at a temperatureof 2°C, or less, and at pressure of 3,000 psi. On SDS-ureaelectrophoresis on acrylamide gel, the actomyosin extracts yieldcomponents of apparent molecular weight 210,000 (myosin heavychains), 47,000 (actin), 35,000 (tropomyosin and/or troponinsubunits), and 13,000 (myosin light chains). The Mg²⁺-ATPaseof Coryphaenoides actomyosin shows a complex Arrhenius plot,with marked denaturation at temperatures above 30°C, anddiminished temperature sensitivity at temperatures below 15°C.Mg²⁺-ATPase is inhibited by pressure, with activation volumesof + 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 overalldata would be consistent with a positive activation volume thatis independent of temperature (to first approximation) and isrelated to the interaction of actin and myosin, and a negativeactivation volume that is temperature dependent and is relateddirectly to activation of myosin ATPase. The net effect appearsto be an adaptive mechanism whereby Mg²⁺-ATPase of Coryphaenoidesactomyosin is relatively insensitive to pressure and temperatureunder conditions encountered by the living fish.