The Effect of pH‐Temperature Treatments on the Calcium Accumulating Ability of Purified Sarcoplasmic Reticulum

SUMMARY: Pig sarcoplasmic reticulum fragments obtained from the longissimus dorsi muscle at 0‐ and 24‐hours post‐mortem were purified by salt extraction and density gradient centrifugation. The calcium uptake activity of 0‐hour purified preparations was more than 20‐fold higher than that from 24‐hr old muscles, but there was no significant difference between fractions for calcium activated ATPase activities. When observed electron microscopically after negative staining, the ultrastructures of the 0. and 24‐hour membrane fragments were found to be essentially identical. Incubation of isolated sacroplasmic reticulum fragments at pH 7.2 and 37°C or pH 5.6 and 0°C caused negligible inhibitoin of their calcium accumulating ability. However, treatment at pH 5.6 and 37°C for 1 hr almost completely abolished the sarcoplasmic reticulum calcium uptake. Thus it appears that low muscle pH and high temperature may be responsible for the inactivation of the calcium accumulating ability of the sarcoplasmic reticulum that occurs in situ.