Effects of Carotenoid Inhibition on the Photosynthetic RC–LH1 Complex in Purple Sulphur Bacterium Thiorhodospira sibirica

Abstract

Core complexes (LH1-RC) were isolated using preparative gel electrophoresis from photosynthetic membranes of the purple bacterium, Thiorhodospira sibirica, grown in the absence or presence of the carotenoid biosynthesis inhibitor, diphenylamine. The biosynthesis of carotenoids is affected by diphenylamine both quantitavely and qualitatively: after inhibition, the level of carotenoids in core complexes reaches only 10% of the normal content, as analyzed by HPLC and absorption spectroscopy. The normally grown bacterium biosynthesizes spirilloxanthin, rhodopin, anhydrorhodovibrin and lycopene, whereas after inhibition only neurosporene, zeta-carotene and their derivatives are found in the complexes. There is no concomitant accumulation of appreciable amounts of colorless carotenoid precursors. Interestingly, the main absorption band of the core light harvesting complex isolated from carotenoid-inhibited cells, shows a red shift to 889 nm, instead of a blue shift observed in many carotenoid-deficient species of purple photosynthetic bacteria. The stability of isolated core complexes against n-octyl-beta-D: -glucopyranoside clearly depends on the presence of carotenoids. Subcomplexes resulting from the detergent treatment, were characterized by non-denaturating gel electrophoresis combined with in situ absorption spectroscopy. Core complexes with the native carotenoid complement dissociate into three subcomplexes: (a) LH1 complexes partially depleted of carotenoids, with an unusual spectrum in the NIR region (lambdamax = 791, 818, 847 and 875 nm), (b) reaction centers associated with fragments of LH1, (c) small amounts of a carotenoidless B820 subcomplex. The core complex from the carotenoid-deficient bacterium is much less stable and yields only the two sub-complexes (b) and (c). We conclude that carotenoids contribute critically to stability and interactions of the core complexes with detergents.

Redox interaction of Mn–bicarbonate complexes with reaction centres of purple bacteria

“…Figure 1a illustrates the absorption spectrum of the pigment-protein complexes B890 isolated from Rh. iodosum which is similar to that isolated previously from other types of purple bacteria (Law et al 2004;Moskalenko et al 2005).…”

Preparative isolation of protein complexes and other bioparticles by elution from polyacrylamide gels

“…On the other side, several groups demonstrate a higher purity of electrophoretically isolated chlorophyll-protein complexes than of the density gradient preparation [297]. There is evidence for the particular mildness of native electrophoresis in the fractionation of photosynthetic complexes (vs. a combination of density-gradient centrifugation with ion-exchange chromatography [298] or solely chromatography [299]). For some proteins, chromatography provides insufficient resolution, while the electrophoretic separation succeeds in a preparative scale [300,301].…”

Spectral properties of LH2 exhibit very similar even when heterologously express LH2 with <i>β</i>-subunit fusion protein in <i>Rhodobacter</i> <i>sphaeroides</i>

“…sphaeroides generally is incapable of forming LH2 [8]. Moreover, blue shifts of light-harvesting complexes will be observed in carotenoid-deficient strains of purple photosynthetic bacteria [25]. However, the mode of Crts binding to LH2 subunits is as yet largely unknown.…”