Rhodopsin regeneration

Moreover, efficient rhodopsin regeneration may precede enzymatic reduction of all-fran.v-retinal to all-trans-retinol in the aged retina (Figure 15.2c) (Schadel et al., 2003). Upon rhodopsin regeneration, all-trans-retinal is released from the exit site of the protein into the lipid membrane (Figure 15.2c) (Schadel et al., 2003). From here the removal of all-tnms-retinal to the outer leaflet of the disc membrane is dependent on activity of ATP-binding cassette trasporter A4 (ABCA4) present in the rim of photoreceptor disc, known also as ABCR protein. 

In these spectra, the protein has been regenerated with retinal specifically 13 C labeled at positions 11,12 and 13, and in each case the retinal resonance exhibits a sharp centerband at the isotropic chemical shift and is flanked by rotational sidebands. Other lines in the spectrum are the natural-abundance 13C resonances of the protein carbonyls ca 175 ppm) and aliphatic carbons (0-100 ppm). Contributions from the Ammonyx-LO detergent in these spectra are seen in the different intensities in the 0-100 ppm region. Ammonyx-LO does not exhibit NMR resonances above 100 ppm. Spectra of the 9-cis pigment isorhodopsin are similar. Table 38 summarizes the isotropic chemical shifts from the solid-state NMR spectra of rhodopsin regenerated with retinal13 C labeled at each position along... 

Chen P, Hao W, Rife L, Wang XP, Shen D, Chen J, Ogden T, Van Boemel GB, Wu L, Yang M, and Fong HK (2001) A photic visual cycle of rhodopsin regeneration is dependent on Rgr. Nature Genetics 28, 256-60. 

The following distinct steps are probably involved in rhodopsin regeneration after a massive bleach (1) mobilization of retinoid in the RPE (2) transport and delivery of retinoid to the retina (3) isomerization of retinoid and its utilization in the ROS. Steps (2) and (3) do not necessarily occur in that order. 

Rhodopsin regeneration has been determined by extracting it directly or by measuring the spectrum of the intact retina. The recovery of ERG sensitivity has also been used as an index of rhodopsin regeneration by Pepperberg and his colleagues. 

Of particular interest is the fact that 11-c/s-ietinoid in bovine retina cytosol consists of 11-cis-retinol as well as 11-cw retinaldehyde. In contrast, only 11-c/s-retinaldehyde is present in the RPE cytosol [Saari (1982) Saari et al. (1982) see also Liou et al. (1982c)]. Since bovine and other mammalian retinas cannot utilize 1 l-cu-retinol for rhodopsin regeneration (see Section III,G,3), its... 

It is supposed that LDH-E plays a role in the regulation of this process in the following ways (1) if NAD becomes a limiting factor in rhodopsin regeneration, LDH may play a role in converting NADH to NAD" (2) the high substrate affinity of LDH-E4 makes possible the utilization of low concentrations of lactate as an energy resource by photoreceptor cells (Whitt et al., 1973 a, b). 

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