Retinoid processing in retinal pigment epithelium of toad (Bufo marinus).
The formation of 11-cis-[3H]retinal in the retinal pigment epithelium (RPE) and its release to extracellular medium containing interphotoreceptor retinoid-binding protein (IRBP) were studied in the RPE eyecup of the toad (Bufo marinus). The RPE was labeled with all-trans-[3H]retinol during an initial 1-h incubation. In phase 2 of the incubation (0-2 h), the extracellular medium contained initially ligand-free IRBP (0-26 microM). Retinoids subsequently extracted from the extracellular medium and RPE were analyzed by high performance liquid chromatography and scintillation counting. IRBP increased both the molar amount and specific radioactivity of 11-cis-retinal released by the RPE during phase 2. The molar amount of 11-cis-retinal in the RPE was small relative to that of retinal released with high IRBP. With 21 microM IRBP and phase 2 incubations of > or = 10 min, the specific radioactivity of released 11-cis-retinal exceeded that of all-trans-retinyl ester in the RPE. The specific radioactivity of 11-cis-retinyl ester was less than that of all-trans-ester, independent of IRBP concentration. The results indicate that IRBP promotes the formation (from all-trans-precursor) as well as the release of 11-cis-retinal and suggest the preferred utilization of recently incorporated and esterified all-trans-retinol in 11-cis-retinal synthesis in a "last in/first out" manner.
Okajima
T I
TI
Department of Ophthalmology and Visual Sciences, University of Illinois, Chicago College of Medicine 60612.
Wiggert
B
B
Chader
G J
GJ
Pepperberg
D R
DR
D000818:Animals; D002024:Bufo marinus; D002851:Chromatography, High Pressure Liquid; D010857:Pigment Epithelium of Eye / Q000378:metabolism*; D012172:Retinaldehyde / Q000302:isolation & purification / Q000378:metabolism; D012176:Retinoids / Q000378:metabolism*; D012177:Retinol-Binding Proteins / Q000378:metabolism*; D012588:Scintillation Counting
D012176:Retinoids; D012177:Retinol-Binding Proteins; D012172:Retinaldehyde