Comparative studies on the tryptic digestion of actomyosins and myosins from several fish species. II. Changes in Ca2+ and EDTA-ATPases.

Abstract

Ca2+- and EDTA-ATPase of actomyosins from several fish species and rabbit were assayed during digestion with trypsin. In typical experiments, the initial activation as well as the inactivation with increasing trypsin concentration were confined to the shorter durations. During digestion, Ca2+- ATPase of heat denatured samples of bigeye tuna and carp actomyosins showed patterns which were identical with those of their respective fresh preparations. A higher initial activation was a general feature of the tuna actomyosins, if the assay of Ca2+- ATPase was performed in 60mM KCl. The initial activation of tilapia actomyosin Ca2+- ATPase was of a lesser extent, whereas it was absent from carp, yellowtail and flatfish actomyosins. At the higher KCl concentration (500mM) in the ATPase assay, the response of Ca2+- ATPase was altogether monophasic i.e. devoid of any initial activation even in the case of rabbit actomyosin. EDTA-ATPase pattern of actomyosin digestion by trypsin closely resembled the pattern of Ca2+- ATPase at the higher KCl concentration. The activation of myosin Ca2+- ATPase of tuna species occurred to a lesser extent than that of actomyosin ATPase, and the reversal of the order of stability observed in case of actomyosin ATPase of tilapia and skipjack tuna was no longer noted. In the light of published work, the reasons for these discrepancies have been discussed.