Regeneration of Rhodopsin and Bacteriorhodopsin

Abstract

The rate of regeneration of rhodopsin, from I I-cis-retinal and opsin, and bacteriorhodopsin from all-transretinal and bacterio-opsin, in the presence or absence of compounds whose structures partially resemble retinal were measured. Some of these compounds severely slowed down the regeneration process, but did not influence the extent of regeneration. In the case of compounds with a carbonyl functional group they were not joined to the active site of the apo-protein via a Schiffs base linkage since after treatment with NaBH4 an active apo-protein remained. The most effective inhibitors of rhodopsin regeneration were molecules whose structure could be superimposed on 9 4 or 11-cis retinal up to carbon atom 11. These C13 and CIS molecules were not distinguished between aldehyde, ketone or alcohol functional groups.The regeneration of bacteriorhodopsin was not inhibited by retinal analogues with short side chains. The most effective inhibitors were the all-trans C1 d d e h y d e (j-ionylideneacetaldehyde) or c 1 8 -ketone (/I-ionylidenepent-3-ene-2-one) which, compared to retinal, lack two or three carbon atoms from the end of the polyene chain. The inhibition was very dependent upon the presence of the all-trans isomer and required aldehyde or ketone as functional group; nitriles and alcohols were less effective. However, similarly to retinol, the all-trans CI7 and c 1 8 alcohols underwent a bathochromic shift and showed fine-structured spectra when mixed with bacterio-opsin

Bacteriorhodopsins with chromophores modified at the β‐ionone site

“…On the other hand omission of both the six-membered ring and the double bond corresponding to the 5,6 double bond in retinal in the chromophore of bR(2) -bR (4) completely destroys the proton pump activity and causes the instability of these pigments in the presence of added all-trans retinal. The omission of only the 5,6 double bond in the bR chromophore does not destroy the proton pump capacity since the bR analogues formed from 5,6-dihydroretinal [22] and CIretinal [23] do display this capacity. Our results demonstrate thus that either the 5,6 double bond or the 2,2,6-trimethyl cyclohexyl ring in the bR chromophore are necessary for the light-driven proton pump function of bR.…”

Methoxyretinals in bacteriorhodopsin

“…The comparison of the reconstitution rates of BRs containing retinal, 13-ethyl retinal or 13-niethoxy retinal under pseudo-first-order conditions [30] allows a more detailed description. From an incubation of a 16 pM bacterioopsin suspension (1 ml volume) with an excess of retinal, 13-ethyl retinal and 13-methoxy retinal, the following BR formation rates were determined (as initial velocities): retinal 4.8 nmol x min-' (l0Oo/~),>, 13-ethyl retinal 1.66 nmol x min-' (35%) and 13-methoxy retinal 0.042 nmol x min-' (0.9%).…”

“…The similarity of the results of 13-demethyl BR [23] and 9-methoxy 13-demethyl BR (compound IV) emphasizes that the region around the double bond 13 -14 is most sensitive to changes of the molecular structures. Alterations closer to the middle of the polyene chain or in the ring region are less important for functional aspects, but in some cases heavily influence the absorption properties of such an analogue BR (see [8,231).…”

“…They can also be influenced by special retinal analogues within the binding site [8,9]. (2), and methoxy compounds I- Vll, presented in their most stable configuration.…”

“…The conditions under which the photochemical routes are selected at the branching points depend on the preparation of the sample (humidity or illumination conditions [6, 71). They can also be influenced by special retinal analogues within the binding site [8,9]. in their most stable configuration.…”