IRBP-like proteins in the eyes of six cephalopod species--immunochemical relationship to vertebrate interstitial retinol-binding protein ( IRBP) and cephalopod retinal-binding protein.
SDS polyacrylamide gel electrophoresis and immunoblotting were used to examine soluble proteins from the eyes of six species of cephalopods i.e. Lolliguncula brevis, Sepia officinalis, Octopus maya, Octopus bimaculoides, Rossia pacifica and Loligo opalescens. All species had a protein (" IRBP") with molecular weight virtually identical with vertebrate interstitial retinol-binding protein ( IRBP) averaging 132,400 +/- 700 (n = 6). " IRBP" reacted on nitrocellulose blot transfers with rabbit antibovine IRBP and rabbit antifrog IRBP antibodies. Unlike vertebrate IRBP, cephalopod " IRBP" (from L. brevis) did not bind exogenous retinol or concanavalin A. The N-terminal amino acid appeared to be blocked in samples electroeluted from SDS gels. The antifrog IRBP antibodies also reacted with a series of proteins with molecular weights between 46,000 and 47,000, identified as retinal-binding protein (RALBP) with anti-RALBP antibodies. Anti- IRBP also reacted with pure RALBP prepared from Todarodes pacificus. Occasionally, anti-RALBP antibodies were seen to react weakly with " IRBP" in some cephalopods. We conclude that RALBP, cephalopod " IRBP" and vertebrate IRBP share a common but distant ancestry, and that a protein resembling IRBP appeared before the vertebrates diverged from the invertebrates. Both RALBP and IRBP appear to have analogous functions in shuttling retinoids between rhodopsin and the corresponding isomerizing system, retinochrome in the cephalopods and retinol isomerase in the vertebrates. The function of cephalopod " IRBP" is unknown.[1]References
- IRBP-like proteins in the eyes of six cephalopod species--immunochemical relationship to vertebrate interstitial retinol-binding protein (IRBP) and cephalopod retinal-binding protein. Fong, S.L., Lee, P.G., Ozaki, K., Hara, R., Hara, T., Bridges, C.D. Vision Res. (1988) [Pubmed]
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