Chloroplasts transamination

PEP is carboxylated to oxaloacetate, transaminated to aspartate ar d shunted into the bundle sheath. Aspartate then is transaminated back to oxaloacetate in the mesophyll, reduced to malate by NADH and decarboxylated to pyruvate by NAD-linked malic enzyme in the bundle-sheath mitochondria. There is no net production of NAD(P)H so the chloroplasts have PSII and may be less effective at inhibiting photorespiration. Pyruvate is phosphorylated in the mesophyll back to PEP, using 2 ATP (Fig. 13.18). 

Serine originates in a direct pathway from 3-phosphoglycerate (pathway a, Fig. 24-20) that involves dehydrogenation, transamination, and hydrolysis by a phosphatase. It can also be formed from glycine by the action of serine hydroxymethyltransferase (Eq. 14-30). This occurs in chloroplasts during photorespiration (Fig. 23-37) and also with some methanogens and other autotropic bacteria and methylotrophs (Fig. 

Fig. 2. Biosynthesis of 5-aminolevulinate in some photosynthetic bacteria, in cyanobacteria, higher plants and algae. The tRNA involved has also been called 6-aminolevulinic acid-RNA (6-ALA-RNA), but it appears to be identical to the tRNA used by chloroplasts for translation of chloro-plast mRNA. Chloroplast glutamic acid tRNA liga-ses (glutamyl-tRNA synthetases) have been purified to homogeneity from several sources. The final reaction is an intramolecular transamination, which, like conventional intermoleculartransaminations, requires pyridoxal phosphate.

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