[Carbon isotope (13C/12C) effect of photorespiration in photosynthetic organisms. Evidence for existence, probable mechanism].
Experimental evidence in favor of the new phenomenon predicted for photosynthesizing organisms, the fractionation of carbon isotopes in photorespiration is presented. A possible mechanism of this process is discussed. The fractionation of carbon in isotopes photorespiration occurs in the oxygenase phase of the functioning of ribulosebisphosphate carboxylase/oxygenase (rubisco), the key enzyme of photosynthesis, which is capable to act as carboxylase and oxygenase. Which function of the enzyme is active depends on CO2/O2 concentration ratio, which periodically changes in a cell. The key reaction in the mechanism of carbon isotope fractionation in photorespiration is glycine decarboxylation, which results in the splitting and removal from the cell of CO2 enriched with 12C and the accumulation of 13C photorespiratory carbon flow. The coupling of photorespiration and CO2 photoassimilation gives rise to two isotopically different carbon flows, which fill up separate carbohydrate pools, which are the sources of carbon in the following syntheses in the dark phase of photosynthesis. This enables one to identify, from the carbon isotope ratio of metabolites, their involvement in the photorespiratory and assimilatory carbon flows, to investigate the pathways of carbon metabolism, and to estimate more thoroughly the biosynthetic role of photorespiration.
Ivlev
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AA
Timiryazev Moscow Agricultural Academy, ul. Timiryazevskaya 49, Moscow, 127550 Russia.
D002247:Carbon Isotopes / Q000737:chemistry*; D010788:Photosynthesis; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism
D002247:Carbon Isotopes; D012273:Ribulose-Bisphosphate Carboxylase