FRINK Linked Data Fragments server

Matches in SemOpenAlex for { <https://semopenalex.org/work/W2045831468> ?p ?o ?g. }

• W2045831468 endingPage "111" @default.
• W2045831468 startingPage "95" @default.
• W2045831468 abstract "Extant photosynthetic organisms all appear to use transmembrane H+ fluxes as the coupling agent in the use of light energy in ATP synthesis. In the steady-state there is a large H+ free energy difference across the coupling membrane, and when this is reflected as a light-induced change in pH of the phase (cytosol or stroma) containing the enzymes of carbon assimilation, the H+ transport can have an informational role in activating and inactivating enzymes. The earliest organisms probably lived fermentatively (substrate-level phosphorylation) in an anaerobic environment provided with organic solutes synthesised abiotically. There are good reasons for believing that one of the earliest primary active transport systems (interconverting chemical and electrical/osmotic energy) was an H+ extrusion pump powered by ATP or PPi. Its initial function was extrusion of excess H+ from the fermenting cells, and the support of a number of co-transport processes. The earliest energetic use of light energy is envisaged as being the energization of an alternative H+ extrusion pump, with bacteriorhodopsin or (bacterio-) chlorophyll as the pigment. The former type of cyclic photoredox system (Halobacterium-type) is simpler than the latter: a “pre-respiratory” chemical redox H+ pump may have preceded the (bacterio-) chlorophyll-based process. Any of these H+ pumps could spare the use of fermentative ATP in powering active H+ efflux and would thus have been favoured as fermentative substrates became scarce; eventually the larger ΔμH+ generated by the light-powered H+ pump was used to drive the ATP-powered H+ pump backwards and thus generate ATP with light as the ultimate energy source. Scarcity of suitable reductants for biosynthesis as life proliferated provided a selective impetus for a non-cyclic photoredox system which could use light energy to generate a low-potential reductant at the expense of more readily available higher-potential reductants. The non-cyclic photoredox system is not possible in its simplest form (with all the redox energy coming from excitation energy of one or more photoreactions) in the bacteriorhodopsin line of evolution. Such a simple photoredox system is found in the Chlorobiaceae; even if (as seems likely) the non-cyclic photoredox process generates a ΔμH+ (and thus, potentially, ATP), some of the ATP needed for CO2 fixation and cell growth must be generated by a cyclic photoredox system. In the extant purple bacteria the generation of low-potential reductant involves a non-cyclic photoredox pathway which produces a reductant unable to reduce NAD+; the “energy gap” is spanned by “reverse electron transfer” which uses energy from a ΔμH+. It is not clear if this energetic requirement for the H+ gradient can be quantitatively satisfied from a non-cyclic photoredox H+ transport; it is certain that there is a major requirement for cyclic photoredox H+ pumping in these organisms. The photosynthetic bacteria are today restricted to reducing (low Eh) environments similar to those found in the early, anoxic earth; they are unable to use very weak reductants as donors for non-cyclic photoredox processes. As the sources of even weakly reducing donors (other than H2O) on the primitive earth were depleted the two photoreactions scheme of extant O2-producers evolved by modification of the bacterial photoreaction. This non-cyclic photoredox process is definitely H+-translocating and the role of cyclic photoredox processes in ATP generation in O2-evolvers is smaller than in photosynthetic bacteria. In parallel with the biochemical and biophysical changes in the photosystems there was a morphological evolution, with an increasing tendency for “internalisation” of the photoredox processes (originally present in the plasma membrane, as in extant Chlorobineae) into thylakoids (as in most Rhodospirillineae, Cyanobacteria and in all eukaryotes). With a plasmalemma-located photoredox system, and the constraints of a fixed, alkaline external pH and the cytoplasmic pH of 7–8, the ΔμH+ would be generated largely as an electrical P.D. The presence of a phase (intrathylakoid space) with a “negotiable pH” would permit the generation and use of a ΔμH+ largely present as a pH gradient. In both cases illumination can cause an increase in cytoplasmic (stromal) pH over the dark value; this is an important aspect of the regulation of “phototrophic” and “heterotrophic” enzyme systems in the light and in the dark. However, it is argued that these differences in pH are not absolutely light-dependent unless they depend upon some more uniquely light-dependent signal, probably based on a redox component only generated in the light." @default.
• W2045831468 created "2016-06-24" @default.
• W2045831468 creator A5041675614 @default.
• W2045831468 creator A5045351495 @default.
• W2045831468 date "1981-01-01" @default.
• W2045831468 modified "2023-09-26" @default.
• W2045831468 title "H+ transport in the evolution of photosynthesis" @default.
• W2045831468 cites W1501707669 @default.
• W2045831468 cites W1511891385 @default.
• W2045831468 cites W1697798965 @default.
• W2045831468 cites W1834418945 @default.
• W2045831468 cites W1861812392 @default.
• W2045831468 cites W1963783727 @default.
• W2045831468 cites W1965481808 @default.
• W2045831468 cites W1970405782 @default.
• W2045831468 cites W1971940825 @default.
• W2045831468 cites W1974150249 @default.
• W2045831468 cites W1976383021 @default.
• W2045831468 cites W1985326522 @default.
• W2045831468 cites W1993862191 @default.
• W2045831468 cites W1996798028 @default.
• W2045831468 cites W1997624950 @default.
• W2045831468 cites W2002906402 @default.
• W2045831468 cites W2003212387 @default.
• W2045831468 cites W2006773465 @default.
• W2045831468 cites W2011026683 @default.
• W2045831468 cites W2012906367 @default.
• W2045831468 cites W2014121894 @default.
• W2045831468 cites W2015114647 @default.
• W2045831468 cites W2015166372 @default.
• W2045831468 cites W2016267544 @default.
• W2045831468 cites W2016942442 @default.
• W2045831468 cites W2018466639 @default.
• W2045831468 cites W2019784795 @default.
• W2045831468 cites W2022459079 @default.
• W2045831468 cites W2043436739 @default.
• W2045831468 cites W2050002964 @default.
• W2045831468 cites W2051037340 @default.
• W2045831468 cites W2051867107 @default.
• W2045831468 cites W2052353118 @default.
• W2045831468 cites W2053618778 @default.
• W2045831468 cites W2054949417 @default.
• W2045831468 cites W2067779327 @default.
• W2045831468 cites W2068276476 @default.
• W2045831468 cites W2075949084 @default.
• W2045831468 cites W2076059269 @default.
• W2045831468 cites W2078412003 @default.
• W2045831468 cites W2081892936 @default.
• W2045831468 cites W2092133911 @default.
• W2045831468 cites W2093178840 @default.
• W2045831468 cites W2104225119 @default.
• W2045831468 cites W2104228140 @default.
• W2045831468 cites W2112951169 @default.
• W2045831468 cites W2121103427 @default.
• W2045831468 cites W2124688140 @default.
• W2045831468 cites W2133866431 @default.
• W2045831468 cites W2159432287 @default.
• W2045831468 cites W2166470989 @default.
• W2045831468 cites W2173155886 @default.
• W2045831468 cites W2176247490 @default.
• W2045831468 cites W2407904205 @default.
• W2045831468 cites W64788924 @default.
• W2045831468 cites W72657818 @default.
• W2045831468 doi "https://doi.org/10.1016/0303-2647(81)90025-3" @default.
• W2045831468 hasPubMedId "https://pubmed.ncbi.nlm.nih.gov/7272473" @default.
• W2045831468 hasPublicationYear "1981" @default.
• W2045831468 type Work @default.
• W2045831468 sameAs 2045831468 @default.
• W2045831468 citedByCount "23" @default.
• W2045831468 countsByYear W20458314682012 @default.
• W2045831468 countsByYear W20458314682013 @default.
• W2045831468 countsByYear W20458314682015 @default.
• W2045831468 countsByYear W20458314682016 @default.
• W2045831468 countsByYear W20458314682018 @default.
• W2045831468 countsByYear W20458314682020 @default.
• W2045831468 countsByYear W20458314682022 @default.
• W2045831468 crossrefType "journal-article" @default.
• W2045831468 hasAuthorship W2045831468A5041675614 @default.
• W2045831468 hasAuthorship W2045831468A5045351495 @default.
• W2045831468 hasConcept C112243037 @default.
• W2045831468 hasConcept C12554922 @default.
• W2045831468 hasConcept C171357686 @default.
• W2045831468 hasConcept C181199279 @default.
• W2045831468 hasConcept C183688256 @default.
• W2045831468 hasConcept C185592680 @default.
• W2045831468 hasConcept C189542057 @default.
• W2045831468 hasConcept C41625074 @default.
• W2045831468 hasConcept C55493867 @default.
• W2045831468 hasConcept C86803240 @default.
• W2045831468 hasConcept C90424259 @default.
• W2045831468 hasConceptScore W2045831468C112243037 @default.
• W2045831468 hasConceptScore W2045831468C12554922 @default.
• W2045831468 hasConceptScore W2045831468C171357686 @default.
• W2045831468 hasConceptScore W2045831468C181199279 @default.
• W2045831468 hasConceptScore W2045831468C183688256 @default.
• W2045831468 hasConceptScore W2045831468C185592680 @default.
• W2045831468 hasConceptScore W2045831468C189542057 @default.
• W2045831468 hasConceptScore W2045831468C41625074 @default.

• next