Organelle-specific Isozymes of Aspartate-alpha-Ketoglutarate Transaminase in Spinach Leaves

Four distinct isozymes of aspartate-α-ketoglutarate transaminase in a spinach (Spinacia oleracea L.) leaf extract were separated by starch gel electrophoresis. Of the total aspartate-α-ketoglutarate transaminase activity, approximately 45% was represented by the chloroplast isozyme, 26% by the cytosol isozyme, 19% by the mitochondrial isozyme, and 3 to 10% by the peroxisomal isozyme. The aspartate-α-ketoglutarate transamination activity in the four subcellular compartments behaved similarly. It was freely reversible and α-ketoglutarate was preferred to pyruvate or glyoxylate as the amino group acceptor. With glutamate as the amino group donor, oxaloacetate was superior to pyruvate or glyoxylate as the acceptor in chloroplasts, mitochondria, and cytosol, while pyruvate or glyoxylate was preferred to oxaloacetate as the acceptor in peroxisomes.