MYOSIN SUBFRAGMENT-1 ISOFORMS HAVING DIFFERENT HEAVY-CHAIN STRUCTURESFROM FAST SKELETAL-MUSCLE OF THERMALLY ACCLIMATED CARP

Three heavy chain isoforms of chymotryptic myosin subfragment-1 (S1) w ith different molecular sizes of 96 kDa (H1), 94 kDa (H2), and 92 kDa (H3), were detected in the fast skeletal muscle from thermally acclima ted carp. In total, six S1 isoforms were present, including two S1 iso forms for each heavy chain due to associated A1 and A2 light chains. H 1 heavy chain was dominant in the 10 degrees C-acclimated carp and res ponsible for high acto-S1 Mg2+-ATPase activity and low thermostability . In contrast, H3 heavy chain predominating in the 30 degrees C-acclim ated carp showed low acto-S1 Mg2+-ATPase activity and high thermostabi lity. H2 heavy chain was found in the 10- and 20 degrees C-acclimated fish. H3 heavy chain featured three tryptic fragments with normal mole cular masses of 28, 50, and 20 kDa in order from the N-terminus. Howev er, H1 heavy chain contained an unusual, longer ''20 kDa'' peptide who se molecular size was estimated to be about 23 kDa.