11-cis-Retinal-binding protein from bovine retina. Isolation and partial characterization

Area of Science:

• Biochemistry
• Molecular Biology
• Vision Science

Background:

• The visual cycle involves the regeneration of 11-cis-retinal, a crucial chromophore for photoreceptor proteins.
• Understanding the proteins involved in retinal binding and transport is essential for elucidating visual cycle mechanisms.

Purpose of the Study:

• To purify and characterize the 11-cis-retinal-binding protein from bovine retina.
• To investigate the endogenous ligands associated with the purified binding protein.
• To assess the protein's relationship with opsin and its potential role in the visual cycle.

Main Methods:

• Purification using gel filtration, ion exchange, and hydroxylapatite chromatography.
• Molecular weight determination via SDS-PAGE and gel filtration.
• Spectroscopic analysis (UV-Vis) to identify bound ligands.
• Immunological cross-reactivity tests with anti-bovine opsin antibodies.
• Amino acid composition analysis.

Main Results:

• The 11-cis-retinal-binding protein was purified to homogeneity with molecular weights of 33,000 (SDS-PAGE) and 36,000 (gel filtration).
• The purified protein exhibited absorbance maxima at 340 nm and 425 nm, attributed to bound 11-cis-retinol and 11-cis-retinal, respectively.
• The protein did not cross-react with anti-bovine opsin antibodies and had a distinct amino acid composition.
• Retinal-binding protein was found at approximately 1 nmol/retina or 1 mol per 20 mol of opsin.

Conclusions:

• The purified protein is a distinct entity from opsin, tentatively identified as 11-cis-retinal-binding protein.
• The presence of endogenous 11-cis-retinol and 11-cis-retinal suggests a significant role in the visual cycle.
• Its specificity and abundance indicate a major function in the transport or storage of retinoids within the retina.