Comparative studies on the heavy meromyosin fragments from tilapia dorsal and rabbit skeletal muscles

Attempts were made to prepare heavy meromyosin (HMM) by tryptic digestion of dorsal muscle myosin from tilapia, Tilapia mossambica, and the biochemical properties of HMM from tilapia and rabbit were compared. 1) Results from gel filtration of HMM on a Sephadex G-200 column showed that tilapia myosin was digested by trypsin into smaller fragments more quickly than rabbit skeletal myosin. 2) Various effectors, such as KCl, Ca2+, Mg2+, PCMB, EDTA, actin and pH, showed essentially the same effects on tilapia HMM ATPase activity as on that of rabbit HMM. 3) It was recognized that tilapia HMM combine with F-actin revealed the identical characteristics of rabbit acto-HMM; that is, high ATP-sensitivity and the enhancement of Mg2+-ATPase activity. 4) The most remarkable differences between tilapia and rabbit HMM were observed in the thermo-stability of their Ca2+-ATPase activity. In 0.6M KCl (pH 7.0) the rates of inactivation of HMM from tilapia and rabbit at 30°C were found to be 15.0×10-5 sec-1 and 4.60×10-5 sec-1, which values are comparable to the rates of their respective myosins.