ALL-trans β-CAROTENE-5,6-EPOXIDE IN THYLAKOID MEMBRANES

All- trans β-carotene-5,6-epoxide has been found in the thylakoid membranes of spinach and of the cyanobacterium Synechococcus vulcanus Copeland. The epoxide was extracted from the thylakoid membranes with acetone, and was isolated by high-performance liquid chromatography (HPLC). The structure of the epoxide was identified by means of mass, Raman, and electronic absorption spectroscopy. Changes in the amount of the epoxide, as a result of epoxidation and (apparent) de-epoxidation reactions in the membranes, were traced by analysis of extracts on HPLC. In isolated thylakoid membranes, only the epoxidation reaction took place. The reaction was caused by irradiation or by the addition of ferricyanide, suggesting that electron transport reactions in the membranes are involved in the epoxidation. In intact spinach leaves, however, both epoxidation and de-epoxidation took place; the extent of epoxidation correlated with the intensity of light incident on the leaves. The epoxidation and de-epoxidation of all- trans β-carotene are contrasted with those of xanthophylls (in the violaxanthin cycle).     

FUNCTIONAL PROPERTIES OF CATTLE RHODOPSIN IN SOLUBLE COMPLEX WITH PHOSPHOLIPIDS and DEOXYCHOLATE

Abstract— The necessary conditions of bleached rhodopsin to activate GTPase and to regenerate α-band were studied by changing the number of bound phospholipids to rhodopsin using gel filtration procedure. The number of bound phospholipids per mole of rhodopsin (bPL/rho) in the eluants was reproducibly controlled by the concentration of sodium deoxycholate (DOC) in the elution buffer. The eluants were soluble complexes composed of rhodopsin with original a-band, disk phospholipids and DOC. The regenerability of α-band depended on bPL/rho but neither on the concentration of DOC nor on state of aggregation of rhodopsin. The lowest number of bPL/rho for this activity under our experimental conditions was estimated to be30–50 in bPL/rho. GTPase was activated only by such complexes that had a nearly original quantity of bPL/rho in disk membranes. Other complexes with less bPL/rho showed aggregation upon bleaching and did not activate GTPase. The amount of phospholipids present in the disk membranes is sufficient to prevent aggregation of rhodopsin upon bleaching.     

CO-trapping reaction under thermolysis of alkoxyamines: application to the synthesis of 3,4-cyclopenta-1-tetralones

[reaction: see text] An efficient one-pot sequence comprising a PRE-mediated radical 5-exo-cyclization, a radical carbonylation, a nitroxide trapping reaction, and a subsequent acid-catalyzed Friedel-Craft-type acylation provides a new entry into 3,4-cyclopenta-1-tetralones. Eight examples are presented.     

CONFIGURATIONS OF CAROTENOIDS IN THE REACTION CENTER and THE LIGHT-HARVESTING COMPLEX OF Rhodospirillum rubrum. NATURAL SELECTION OF CAROTENOID CONFIGURATIONS BY PIGMENT PROTEIN COMPLEXES

Abstract— Carotenoids extracted from the reaction center (RC), the light-harvesting complex (LH), and the chromatophore membrane of Rhodospirillum rubrum SI were analyzed by high-performance liquid chromatography. The chemical structures and the configurations of major components were determined by means of mass, Raman, electronic absorption and ¹H-NMR spectroscopy. The results indicated: (1) 15- cis -spirilloxanthin is bound to RC; (2) both all-frans-spirilloxanthin and aII-(ran.s-3,4-dihydrospirilloxanthin are bound to LH and (3) 13-cK-spirilloxanthin is additionally present in the chromatophore membrane. The natural selection of the carotenoid configurations, i.e. 15-ris by RC and aW-trans by LH, is discussed in relation to the physiological functions and the photophysical properties of isomeric carotenoids.