Phosphorylation of interphotoreceptor retinoid-binding protein (IRBP).
The phosphorylation of interphotoreceptor retinoid-binding protein (IRBP), the major soluble (glycolipo) protein of the interphotoreceptor matrix (IPM) and a putative intercellular retinoid-transport vechicle, has been examined in a crude bovine IPM wash using [?-(32)P]ATP. SDS-polyacrylamide gel electrophoresis and autoradiography, size-exclusion high-performance liquid chromatography (HPLC) and ion-exchange HPLC all showed IRBP to be phosphorylated in this system. The phosphorylation probably is of serine and/or threonine residues rather than of tyrosine. Interestingly, phosphorylated IRBP was bound tightly to concanvalin A (Con A)-Sepharose and was not eluted by 50 mM ?-methyl-d-mannoside indicating a marked alteration in binding characteristics upon phosphorylation.
Wiggert
B
B
Laboratory of Retinal Cell and Molecular Biology, National Eye Institute, National Institutes of Health, Bethesda, MD 20892, U.S.A.
Lal Kapoor
C
C
Lee
L
L
Somers
R L
RL
Chader
G J
GJ