Tryptic Fragmentation of the Calcium Transport System in the Sarcoplasmic Reticulum

Abstract

Two protein fragments with a molecular weight of 50-60 000 daltons are formed when the calcium transport ATPase of the SR is mildly digested with trypsin. The initial fragmentation of the ATPase does not interfere with calcium transport, calcium dependent ATPase activity and phosphoprotein formation. The decay of the initially formed protein fragments after prolonged tryptic digestion is accompanied by the decline of the rate of calcium uptake and the calcium concentrating ability while the activity of the calcium activated ATPase is reduced only moderately. The initial tryptic fragmentation does not give rise to any change in the morphological appearance in the SR membranes. After prolonged digestion brush border or smooth surface structures are observed depending on the agent used for negative staining.