Turbidity Increase of Myosin Subfragment-1 from Carp and Rabbit Induced by Heat-treatment

Abstract

Myosin subfragment-l (S-1) of carp was incubated at 30°C in a medium consisting of 0.5M KCl, 20mM Tris-HCl (pH 7.5) and the Ca-ATPase activity and turbidity change were followed. The turbidity of carp S-1 increased as Ca-ATPase activity decreased. Upon centrifugation of thus turbid S-1 solution, the insoluble fraction was obtained as the pellet, and was analyzed by SDS-gel electrophoresis. The turbid component of S-1 was proved to be S-1 heavy chain aggregates dissociating light chains. The elution profile of mildly heated carp S-1 on Sepharose CL-4B gel filtration showed an accumulation of S-1 oligomer, not dimer, which is an intermediate of the turbid form of the S-1 heavy chain aggregates.
These results indicated that the formation of heavy chain aggregates caused the increase in the turbidity of S-1 solution which was accompanied by light chain release. Such denaturations of S-1 as above were found to be delayed in the case of rabbit S-1.