CHARACTERIZATION OF CA2-ATPASE IN ROD OUTER SEGMENT DISK MEMBRANES()

The Ca2+-pump isolated in rod outer segment disk membranes as aspartyl phosphate intermediate E-P has been characterized: the 100 kDa phospho protein was completely inhibited by thapsigargin, was not sensitive to digestion by calpain, and displayed a tryptic digestion pattern with the formation of two autophosphorylatable fragments of about 55 and 35 kDa. These results are typical of the calcium pumps of sarcoplasmic o r endoplasmic reticulum calcium and differ from those of plasma membra ne, such as the Ca2+-ATPase of the red blood cells, here shown as cont rols. The physiological role of calcium pump in disk membranes of vert ebrate photoreceptors is discussed in terms of intracellular calcium b uffering. (C) 1994 Academic Press, Inc.