Effects of proteolysis and mechanism of gel weakening in heat-induced gelation of fish myosin

Addition of papain decreased the onset temperature and the rate at which G' developed during heat-induced gelation of arrowtooth flounder myosin. Freq uency sweep results revealed that G' markedly decreased in proportion to th e amount of papain added. However, use of E-64, a cysteine proteinase inhib itor, reversed the effects of papain and protected myosin heavy chain from degradation. DSC thermograms indicated papain significantly decreased the e nthalpy required to induce myosin denaturation without significant changes in onset and maximum transition temperatures. Thermal denaturation kinetics indicated decreases in both the activation energy and the rate of myosin d enaturation. CD studies revealed a rapid decrease in alpha-helical content, indicating the initial degradation of myosin molecules mostly occurred in the tail region. These results suggested that proteolysis affected thermal properties and reactivity of myosin during heating. Although myosin gel cou ld be formed, structural disruption resulted in lower gelling ability and r igidity of the formed gel.