Glycolate pathway glycine synthesis

Major pathways for the synthesis and interconversion of glycine and serine in plants are outlined in the scheme in Fig. 1. The most studied pathway, the glycolate pathway, is that associated with photosynthesis and responsible for photorespiration (see Tolbert, this series, Vol. 2, Chapter 12). Flux through this pathway is rapid especially in the leaves of C3 plants. Alternatives to the glycolate pathway exist in green and nongreen tissues but because of slower turnover rates evidence for them from experiments using isotopic tracers is less clear and the enzymes concerned are more difficult to study because of their lower concentration in the tissues. 

Minor Pathways. Dihydroxyacetone phosphate can be transformed to glycerol phosphate, which is used for the synthesis of fats and glycerophosphatides. Phosphoglycerate can be converted to 3-phosphohydroxypyruvate and further to hydroxypyruvate. This last compound is possibly related to glycolate (by oxidative decarboxylation) and to glyoxylate, and hence to glycine. Pyruvate is related to alanine by transamination, and hydroxypyruvate, to serine. 

The synthesis and interconversion of these amino acids is intimately related to the photorespiratory pathway in plants (Wallsgrove et ai, 1983b). As illustrated in Fig. 2, glycolate, formed in chloroplasts [(1) and (2)], is oxidized to glyoxylate and converted to glycine in peroxisomes [(3), (4), and (5)]. Glycine is,... 

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