Molecular Properties of Post‐Mortem Muscle.

Abstract

SUMMARY— Post‐mortem changes in nucleoside triphosphatase activity of bovine myosin B have been studied by using several different modifiers with either 5 mM ATP or 5 mM ITP as substrate at ionic strengths (r/2) of 0.09, 0.19, or 0.52. Enzymic activity was determined by measuring the release of inorganic phosphate. There was very little difference in enzymic activity between myosin B isolated from prerigor, rigor (24 hr post‐mortem) or post‐rigor (312 hr post‐mortem) muscle stored at either 2° or 16°C except that the specific activity of myosin B prepared from muscle stored for 12–24, hr post‐mortem was higher than activity of myosin B prepared immediately after death. This increase cannot be explained in terms of rigor shortening, but suggests that a change in myosin conformation or in the nature of the actin‐myosin interaction occurs in post‐mortem muscle. If an actin‐myosin interaction occurs during rigor mortis and if this association remains unchanged during extraction of myosin B, then the very low Mg++‐modified myosin B enzymic activities obtained at Γ/2 = 0.19 and 0.52 indicate that this interaction is not irreversible. Extraction in the absence of ATP produced a myosin B whose ATPase activity was markedly inhibited by trace amounts of Mg++. This may be due to the absence of a‐actinin in these myosin B preparations. No consistent differences in activation energies were found either at Γ/2 = 0.19 or 0.52 among the NTPase reactions of myosin B samples prepared from muscle after various times of post‐mortem storage.