Retinal-based photosynthesis may contribute to the free energy conversion needed for growth of an organism carrying out oxygenic photosynthesis, like a cyanobacterium. After optimization, this may even enhance the overall efficiency of phototrophic growth of such organisms in sustainability applications. As a first step towards this, we here report on functional expression of the archetype proteorhodopsin in Synechocystis sp. PCC 6803. Upon use of the moderate-strength psbA2 promoter, holo-proteorhodopsin is expressed in this cyanobacterium, at a level of up to 10 5 molecules per cell, presumably in a hexameric quaternary structure, and with approximately equal distribution (on a protein-content basis) over the thylakoid and the cytoplasmic membrane fraction. These results also demonstrate that Synechocystis sp. PCC 6803 has the capacity to synthesize alltrans-retinal. Expressing a substantial amount of a heterologous opsin membrane protein causes a substantial growth retardation Synechocystis, as is clear from a strain expressing PROPS, a nonpumping mutant derivative of proteorhodopsin. Relative to this latter strain, proteorhodopsin expression, however, measurably stimulates its growth.
Durch Verbrennungskalorimetrie wird die Bildungsenthalpie des Benzocyclobutens (2)zu AH: (g) = 199.4 kJ mol-' (47.7 kcal mol-') bestimmt. Aus der Kinetik der Reaktion von 2 mit Maleinsaureanhydrid (MSA) ergeben sich fur die o-Chinodimethanbildung 2 + 1 Aktivierungsparameter E, = 166.9 kJ mol-' (39.9 kcal mol-'), A = 2.8 x IOl4 s-', Die entsprechenden Werte der Ruckreaktion 1 + 2 werden aus der Dimerisierungsgeschwindigkeit des Benzocyclobutens sowie der durch Blitzlichtphotolyse von 5,6-Dimethylenbicyclo[2.2.l]hept-2-en-7-on (5) ermittelten Geschwindigkeitskonstanten der o-Chinodimethandimerisierung zu E, = 122.7 kJ mol-' (29.3 kcal mol-'), A = 2.2 x IOl3 s-', bestimmt.
Energy Profile of the o-Quinodimethane-Benzocyclobutene EquilibriumThe enthalpy of formation of benzocyclobutene (2) is measured by combustion calorimetry to be AHp(g) = 199.4 kJ mol-' (47.7 kcal mol-'). From the kinetics of the reaction of 2 with maleic anhydride the activation parameters for the o-quinodimethane formation 2 + 1 are obtained: E, = 166.9 kJ mol-' (39.9 kcal mol-'), A = 2.8 x I O l 4 s-'. The corresponding values for the back reaction 1 + 2 are derived from the dimerisation rate of o-quinodimethane, obtained by flash photolysis of 5,6-dimethylenebicyclo[2.2.l]hept-2-en-7-one (S), and from the dimerisation of benzocyclobutene yielding E, = 122.7 kJ mol-' (29.3 kcal mol-I),o-Chinodimethan (1) kann, wie seine Resonanzstruktur 1 b anzeigt, als hoch stabilisiertes Diradikal aufgefal3t werden. Im Hinblick auf die Diskussion uber die Lage von Diradikalen auf der Reaktionskoordinate ') ist es von Interesse, das Energieprofil der Cyclisierung des o-Chinodimethans (1) zu Benzocyclobuten (2) zu ermitteln. Dieses wird durch ') L. Salem und C. Rowland, Angew. Chem. 84, 86 (1972); Angew. Chem., Int. Ed. Engl. 11, 92 (1972).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.