CARP EXPRESS SPECIFIC ISOFORMS OF THE MYOSIN CROSS-BRIDGE HEAD, SUBFRAGMENT-1, IN ASSOCIATION WITH COLD AND WARM TEMPERATURE-ACCLIMATION

1. The 81 fragment is the head of the myosin cross-bridge which is the force generator for muscle contraction and has actin binding and ATPa se sites. The latter is believed to determine the rate of myosin cross -bridge cycling and hence power production by the muscle fibres. 2. Po lyacrylamide gel electrophoresis in the presence of sodium pyrophospha te (PPi-PAGE) showed that carp acclimated to 10 degrees C contained fo ur isoforms of chymotryptic myosin Sl in fast skeletal muscle. Peptide mapping revealed that these consisted of two types of S1 heavy chain, H1 and H2, with different primary structures. Four S1 isoforms in tot al, H1 (A1), H1 (A2), H2 (A1), and H2 (A2), were separated in PPi-PAGE with two associated light chains, A1 and A2. 3. Fish acclimated to 30 degrees C contained another type of S1 heavy chain, H3, and thus incl uded two S1 isoforms, H3 (A1) and H3 (A2). 4. These results suggest a possible genetic regulation for different S1 isoform expression in an acclimation temperature-dependent manner.