Structure and function of sarcoplasmic reticulum isolated from slowly and from rapidly-glycolysing skeletal muscle

There is evidence that sarcoplasmic reticulum isolated from muscle that has undergone a rapid post-mortem decline in pH has impaired calcium-accumulating ability when compared with that from normal muscle which has a slow rate of pH decline (Greaseret al., 1969a). The enzyme responsible for translocating the cations, namely the ATPase protein, was less affected. The implication is that ATP hydrolysis has been uncoupled from vectorial transfer of calcium through the reticular membrane. This study establishes the quantitative differences in calcium transport and ATPase activity of fragmented sarcoplasmic reticulum from the two muscle sources and has attempted to determine the nature of the diminished efficiency of sarcoplasmic reticular vesicles from muscles of diseased animals. In view of the membrane-bound nature of the pump protein, the influence of the lipid environment on its functional activity was considered and a detailed analysis of the lipids of the sarcoplasmic reticular membrane was carried out. The lipid studies included on analysis of whole muscle since a general derangement of muscle cell membranes is inferred in this disease from the diffusion of proteins and ions out of the muscle cell into the extracellular fluid. In addition, the nature of the lipid-ATPase interaction was examined by observing the effect of temperature on the functional activities of the sarcoplasmic reticulum