LOWER ACTIVATION-ENERGY FOR SLIDING OF F-ACTIN ON A LESS THERMOSTABLEISOFORM OF CARP MYOSIN

We have examined the temperature-dependence of sliding velocity of flu orescent F-actin on myosins isolated from 10 degrees C- and 30 degrees C-acclimated carp, Activation energies for the sliding of F-actin wer e 63 and 111 kJ/mol for the 10 degrees C- and 30 degrees C-acclimated carp myosins, respectively, Arrhenius plots of the sliding velocity fr om 10 degrees C- and 30 degrees C-acclimated carp myosin were shown to intersect at high temperature (about 30 degrees C). The thermostabili ty estimated by measuring the Ca2+-ATPase activity was less for myosin from 10 degrees C- than 30 degrees C-acclimated carp, We suggest that a less thermostable structure in cold-acclimated carp myosin results in a reduced activation energy for the contractile process, which allo ws the F-actin to slide fast even at low temperatures.