© 1971 by The Society for Integrative and Comparative Biology
Contractile Proteins of a Benthic Fish. II. Composition and ATPase Properties of Actomyosin
Department of Physiology, University of California California, Los Angeles, California 90024
Department of Medicine and Program in Biophysics, State University of New York Downstate Medical Center Brooklyn, New York 11203
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.