C4 photosynthesis (C4 cycle; Hatch-Slack pathway)

A variant of C3 photosynthesis in which CO2 is first concentrated at the site of photosynthesis by carboxylation of phosphoenolpyruvate to oxaloacetate, which is then transported as such or as an interchangeable 4-carbon dicarboxylic acid to the site of photosynthesis. This is an advantage to the plant because the key enzyme, ribulose bisphosphate carboxylase, which in photosynthesis forms 2 mol of 3-phosphoglycerate, has a competing activity, O2 photorespiration, which produces both 3-phosphoglycerate and phosphoglycolate. (see also C3-C4 photosynthesis)Rawsthorne, S. (1992) Essays Biochem. 27, 135-146

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