Comparison of isolated sarcoplasmic reticulum from bovine and rabbit muscle

Comparison of the ultrastructure of purified bovine sarcoplasmic reticulum (SR) vesicles isolated from bovine sternomandibularis muscle before and following cold shortening indicates that the decreased Ca(2+)-accumulating ability and increased release of Ca(2+) in cold shortened muscle are not associated with any apparent structural alterations. Sodium dodecyl sulphate (SDS)-gel profiles revealed that the major constituent in both bovine and rabbit SR was Ca(2+)-activated ATPase with a molecular weight of 100,000-105,000. Both SR preparations also showed a proteolipid band at a molecular weight of approximately 10,000. Purified rabbit SR contained three protein components with molecular weights of 75,000, 60,000 and 53,000, whereas bovine SR exhibited a series of five components with molecular weights of 80,000, 66,000, 63,000, 50,000 and 45,000. Although the functions of these isolated proteins were not determined, it is assumed that at least some of them bind Ca(2+) ions in the SR.