FURTHER-STUDIES ON ADAPTATION OF FISH MYOFIBRILLAR ATPASES TO DIFFERENT CELL TEMPERATURES

Previous studies on fish Mg2+ Ca2+ activated myofibrillar ATPases were extended to species inhabiting diverse thermal environments. Cold adapted ATPases had considerably higher catalytic centered activities at low temperatures than warm adapted ATPases. Differences in cell temperature lead to evolutionary modifications in thermodynamic activation parameters. The free energies, enthalpies and entropies of activation of the Mg2+ Ca2+ myofibrillar ATPase were positively correlated with adaptation temperature. Myofibrils with CaATP-2 as substrate in the absence of Mg2+ will hydrolyze ATP by a mechanism not associated with fibril shortening. Differences in activation enthalpies (.DELTA.HH) between cold and warm adapted Ca2+-activated myofibrillar ATPases were less pronounced than for the physiological ATPase. The Ca2+-activated ATPase showed no relationship between environmental temperature and substrate turnover number or free energy of activation.