Vitamin A is delivered to retinal pigment epithelium cells (RPE) as the alcohol form. Regeneration of visual pigments requires retinoid isomerization, oxidation of the alcohol to the aldehyde form, and delivery of specific retinoid forms to the retina. A """"""""visual cycle"""""""" involving suttling of retinoids from phororeceptor outer segments (ROS) to RPE and back again during cycles of light and dark exposure is known to exist in the eye. This movement requires transfer of retinoids, which are poorly soluble in water, through an aqueous phase, the interphotoreceptor matrix (IPM). It had been suggested, therefore, that the interphotoreceptor retinoid binding protein (IRBP), a soluble IPM protein that binds retinoids, serves as a delivery vehicle in this cycle. The overall goal of this project is to study the mechanism by which retinoids are transported inside the eye an the role of IRBP in this process. To investigate these questions, the physical-chemical characteristics of the interactions of all-trans- and 11-cis-retinol and retinaldehyde with the various environments which they encounter in the eye: cellular membranes, binding protein and water will be studied. The rate constants of the dissociation and association of retinoids interacting with synthetic lipid bilayers, with the outer membranes of RPE and ROS, and with IRBP will be measured. Equilibrium binding affinities and the thermodynamic properties of binding of retinoids to these phases will also be studied. Rates of direct transfer of retinoids between IRBP and the membranes will be measured in order to clarify whether such transfer occurs spontaneously, or whether direct interactions between IRBP and the membranes of target cells at either end of the IPM play a role in the in situ movement of retinoids. The process of diffusion of retinoids in aqueous phases will be studied in detail. Diffusion constants of retinoids will be measured in the presence of various concentrations of proteins and dextrans (macromolecules that do not bind retinoids) to clarify the effects of the properties of an aqueous phase (e.g. viscosity, presence of obstructing macromolecules) on retinoid diffusion. The effects of IRBP and of serum albumin (a """"""""non-specific"""""""" retinoid binding protein) on diffusion under various conditions will be studied. These studies will establish the factors that determine rates and extents of retinoid distribution in the eye and will help to clarify parameters that govern the diffusion of small hydrophobic ligands in aqueous phases in vivo.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
1R01EY009296-01
Application #
3266691
Study Section
Visual Sciences A Study Section (VISA)
Project Start
1991-08-01
Project End
1994-07-31
Budget Start
1991-08-01
Budget End
1992-07-31
Support Year
1
Fiscal Year
1991
Total Cost
Indirect Cost
Name
Weill Medical College of Cornell University
Department
Type
Schools of Medicine
DUNS #
201373169
City
New York
State
NY
Country
United States
Zip Code
10065
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Noy, N (2000) Retinoid-binding proteins: mediators of retinoid action. Biochem J 348 Pt 3:481-95
Noy, N (1998) Measurement of rates of dissociation of retinoids from the interphotoreceptor retinoid-binding protein. Methods Mol Biol 89:177-89
Tschanz, C L; Noy, N (1997) Binding of retinol in both retinoid-binding sites of interphotoreceptor retinoid-binding protein (IRBP) is stabilized mainly by hydrophobic interactions. J Biol Chem 272:30201-7
Chen, Y; Houghton, L A; Brenna, J T et al. (1996) Docosahexaenoic acid modulates the interactions of the interphotoreceptor retinoid-binding protein with 11-cis-retinal. J Biol Chem 271:20507-15
Noy, N; Kelleher, D J; Scotto, A W (1995) Interactions of retinol with lipid bilayers: studies with vesicles of different radii. J Lipid Res 36:375-82
Saari, J C; Bredberg, D L; Noy, N (1994) Control of substrate flow at a branch in the visual cycle. Biochemistry 33:3106-12
Chen, Y; Noy, N (1994) Retinoid specificity of interphotoreceptor retinoid-binding protein. Biochemistry 33:10658-65
Chen, Y; Saari, J C; Noy, N (1993) Interactions of all-trans-retinol and long-chain fatty acids with interphotoreceptor retinoid-binding protein. Biochemistry 32:11311-8
Noy, N; Slosberg, E; Scarlata, S (1992) Interactions of retinol with binding proteins: studies with retinol-binding protein and with transthyretin. Biochemistry 31:11118-24