Nakamura Y, Tolbert N E
J Biol Chem. 1983 Jun 25;258(12):7631-8.
Two different aminotransferases, that have glyoxylate as the amino acceptor, have specific activities of 1 to 2 mumol . min-1 . mg of protein-1 in the isolated peroxisomal fraction from spinach leaves. Their properties were evaluated after separation on a hydroxylapatite column. Both enzymes had a Km for glyoxylate of 0.15 mM and an amino acid Km of 2 to 3 mM. Reactions proceeded by a Ping Pong Bi Bi mechanism. Serine:glyoxylate aminotransferase was relatively specific for both substrates and could only be slightly reversed with 100 mM glycine, although the Ki of glycine was 33 mM. The glutamate:glyoxylate amino-transferase protein was equally active in catalyzing an alanine:glyoxylate aminotransferase reaction, but the reverse reactions with 100 mM glycine were hardly measureable, although the Ki (glycine) was 8.7 mM. Protection against hydroxylamine inhibition from reaction with pyridoxal phosphate was used to investigate the specificity of amino acid binding. Substrate amino acids protected at about the same concentration as their Km, while glycine protected at its Ki concentration. Thus, the nearly irreversible catalysis with glycine is not due to a failure to bind glycine. The significance of a peroxisomal alanine:glyoxylate aminotransferase activity has not been incorporated into schemes for the oxidative photosynthetic carbon cycle.
两种以乙醛酸作为氨基受体的不同转氨酶，在从菠菜叶中分离得到的过氧化物酶体组分中的比活性为1至2 μmol·min⁻¹·mg蛋白质⁻¹。在羟基磷灰石柱上分离后对它们的性质进行了评估。两种酶对乙醛酸的Km为0.15 mM，对氨基酸的Km为2至3 mM。反应通过乒乓双双机制进行。丝氨酸：乙醛酸转氨酶对两种底物相对具有特异性，用100 mM甘氨酸时只能轻微逆转，尽管甘氨酸的Ki为33 mM。谷氨酸：乙醛酸转氨酶蛋白在催化丙氨酸：乙醛酸转氨酶反应中同样具有活性，但用100 mM甘氨酸时的逆反应几乎无法测量，尽管Ki（甘氨酸）为8.7 mM。利用防止与磷酸吡哆醛反应产生的羟胺抑制作用来研究氨基酸结合的特异性。底物氨基酸在与其Km大致相同的浓度下受到保护，而甘氨酸在其Ki浓度下受到保护。因此，与甘氨酸的近乎不可逆催化并非由于未能结合甘氨酸。过氧化物酶体丙氨酸：乙醛酸转氨酶活性的意义尚未纳入光合氧化碳循环的方案中。
