Thermal denaturation profiles of catfish and tilapia myofibrils as affected by pH for heating

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Thermal denaturation profiles of catfish myosin when heated as myofibrils (Mf) were compared with those of tilapia ones. Ca2+-ATPase inactivation rate of catfish myofibrils was the same as that of tilapia myofibrils. The conclusion was the same with isolated myosin. Catfish Mf was clearly distinguished form tilapia Mf in subfragment-1 (S-1) and rod denaturation. A quick denaturation of rod relative to S-1 was characteristic for catfish Mf while a slower denaturation of rod relative to S-1 was the pattern of tilapia Mf. These patterns were greatly affected by the pH for heating. With increasing the pH for heating, rod denaturation was accelerated and oppositely suppressed by lowering the pH for both Mf. Tilapia Mf showed a similar S-1 and rod denaturation pattern to catfish Mf by increasing 1 pH unit. For example, a pattern with catfish Mf at pH 7.5 was similar to one with tilapia Mf at pH 8.5. Less rigid filament structure of catfish Mf than tilapia Mf was demonstrated by studying chymotryptic digestion at various pH. Accordingly, difference S-1/rod denaturation pattern for two fish species was explained by the different rigidity of myosin filaments.