Abstract
Sarcoplasmic reticulum with calcium transport activity has been isolated from the cross-striated adductor muscle of the scallop, which lives in cold (≤20°C) sea water, by using pH 7.0 buffer solution both to homogenize the tissue and to sediment the membrane fraction. The yield of the preparation was 60-100mg protein from 100g of the scallop muscle. Ca2+-activated ATPase protein of about 100 kDa accounted for 40-50% of the protein preparation. The maximum activities of ATP-dependent, oxalate-facilitated calcium accumulation and Ca2+-ATPase were observed at a pH of about 7.0 and temperature of 20-30°C, and their values were about 2μmol Ca2+/mg of protein/min and about 3μmol ATP hydrolysis/mg of protein/min, respectively. At 0°C, 10-20% of these activities was maintained, while at 37°C, the activities were irreversibly lost. The Ca2+-ATPase activity was half-maximally activated at about 0.3μM [Ca2+]. The ATPase activity exhibited non-Michaelian behavior with respect to ATP, with two different Km values of _??_10μM and 0.1-0.3mM. GTP, CTP, and ITP were also hydrolyzed by the preparation at a rate of 10-30% of that of ATP. The preparation was stored at -80°C with retention of function for about a year.
