Abstract
A set of proteins in bovine rod outer segments is specifically methylated by S-adenosyl-L-methionine. The reaction can be demonstrated in the intact retina as well as in fragmented preparations of isolated rod outer segments. The apparent molecular weights of these proteins are 88,000, 61,000, and a subset between 21,000 and 26,000. The Mr = 88,000 protein is shown to be the alpha subunit of the rod outer segment cGMP phosphodiesterase by peptide mapping, two-dimensional gel electrophoresis, the ionic strength dependence of its interaction with the membrane, and immunoprecipitation by antiserum raised against purified phosphodiesterase. For each of these proteins, the incorporated methyl groups are hydrolyzed in alkali to yield methanol, indicating that the proteins are carboxymethylated.
Highlights
A setof proteins in bovine rod outer segments is EXPERIMENTALPROCEDURES methylated by S-adenosyl-L-methionine
Shown to be the
We have shown the M, = 88,000 protein to be the CY subunit of the cGMP phosphodiesterase present inrod outersegmentsanddemonstratedthatthe methylation occurs by esterification of carboxylgroups in Retina-Retinal proteins were labeled according to the protocol of O’Brien et al [18] as described in further detail by Baehr et al [14]
Summary
A setof proteins in bovine rod outer segments is EXPERIMENTALPROCEDURES methylated by S-adenosyl-L-methionine. For each of these proteins, the incorporated methy groups are hydrolyzed in alkali to yield methanol, indicating that the proteins are methionine from New England Nuclear. Retinal proteins were labeled in situ with ["S]methionine, and rod outer segments were isolated as described above The transfeorf the methyl group can be inhibited by heating the membrane preparation to 100 "C before incubating it with AdoMet (Fig. lb, lane 4 )
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