Varieties of rhodopsin in frog rod outer segment membranes: analysis by isoelectric focusing

Purified ROS membranes from cattle, R. pipiens and R. catesbeiana adults and tadpoles were investigated by analytical and preparative isoelectric focusing and SDS-polyacrylamide gel electrophoresis. The rhodopsin from single specimens of R. pipiens displayed two closely-spaced bands with Mr at 34.7 and 37.0 k on SDS polyacrylamide gels. Both were found to be phosphorylated when prepared from retinas incubated with 32Pi and then exposed to light. When purified ROS membranes were solubilized in octyl glucoside and examined by isoelectric focusing followed by SDS-polyacrylamide gel electrophoresis, the low-Mr component focused in two bands (I, IIa) at pH 8.8 and 8.1. Band I and a trace amount of band IIa were observed if band I was eluted and refocused. The high-Mr component focused in one band (IIb) at pH 8.0. Identical isoelectric focusing patterns were observed with ROS membranes from R. catesbeiana tadpoles and the dorsal and ventral retina areas from R. catesbeiana adults. Bovine rhodopsin, on the other hand, had a single Mr component and focused in a major band at pH 6.2.