Suppressive effect of ATP on the denaturation of sarcoplasmic reticulum (Ca2+)-ATPase from southern bluefin tuna Thunnus maccoyii and its biochemical properties

Abstract

Sarcoplasmic reticulum (SR) was prepared from ordinary white muscle of southern bluefin tuna. The chymotryptic digestibility, pH and temperature dependent Ca2+-ATPase activity of SR, as well as the thermal and freezing stability with different additives including ATP were examined. A major component of SR Ca2+-ATPase, which was about 100 kDa by SDS-PAGE analysis, was digested to 60 kDa and 38 kDa fragments by α-chymotrypsin. The SR Ca2+-ATPase activity was 0.3 μmol Pi/min/mg at 25 °C. There was no break point in the Arrhenius plot of temperature-dependent Ca2+-ATPase activity. The activation energy of Ca2+-ATPase was 35.44 kJ/mol. The pH dependence of SR Ca2+-ATPase activity of southern bluefin tuna showed a clear peak with a maximum activity at pH 6.5, and SR Ca2+-ATPase was half inactivated when heated at 45 °C for 4 min. SR Ca2+-ATPase was almost inactivated by pH 5.5 acid treatment, for 2 h at 0 °C. Denaturation by acid treatment was strongly suppressed by the addition of 2 mM ATP. ATP also showed a strong suppressive effect against denaturation of SR Ca2+-ATPase by freezing and heating. These results indicate that ATP reduces denaturation of SR Ca2+-ATPase and that enhancement of ATP levels during freezing has the potential to improve meat quality.