Varticovski L, Kushner J P, Burnham B F
J Biol Chem. 1980 Apr 25;255(8):3742-7.
Bovine liver mitochondria have been found to contain an enzyme which will catalyze the formation of delta-aminolevulinic acid via a transamination reaction rather than via the condensation of glycine and succinyl coenzyme A. The enzyme, L-alanine: gamma,delta-dioxovaleric acid aminotransferase (gamma,delta-dioxovalerate transaminase) was isolated and purifed to apparent homogeneity. gamma,delta-Dioxovalerate transaminase is quite stable, has optimal activity at pH 6.9, requires pyridoxal phosphate as a cofactor and has an apparent molecular weight of 240,000. The enzyme has high specificity for both substrates. The Km for L-alanine is 3.7 x 10(-3) M and the Km for gamma,delta-dioxovalerate is 2.4 x 10(-4) M. Plots of 1/gamma,delta-dioxovalerate against 1/v at varying alanine concentrations suggested a ping-pong reaction mechanism. Although the enzyme appeared to be a typical transaminase, exhaustive experiments failed to demonstrate reversibility of the reaction. The capacity of gamma,delta-dioxovalerate transaminase to synthesize delta-aminolevulinic acid appears to be far greater than the capacity of delta-aminolevulinic acid synthase from the same source. The possibility that gamma,delta-dioxovalerate transaminase plays a role in the biosynthesis of delta-aminolevulinic acid in vivo must be considered.
已发现牛肝线粒体含有一种酶，该酶可通过转氨反应而非甘氨酸和琥珀酰辅酶A的缩合反应催化δ-氨基乙酰丙酸的形成。该酶，L-丙氨酸：γ,δ-二氧戊酸转氨酶（γ,δ-二氧戊酸转氨酶）被分离并纯化至表观均一。γ,δ-二氧戊酸转氨酶相当稳定，在pH 6.9时具有最佳活性，需要磷酸吡哆醛作为辅因子，表观分子量为240,000。该酶对两种底物都具有高度特异性。L-丙氨酸的Km为3.7×10⁻³M，γ,δ-二氧戊酸的Km为2.4×10⁻⁴M。在不同丙氨酸浓度下，以1/γ,δ-二氧戊酸对1/v作图表明是乒乓反应机制。尽管该酶似乎是一种典型的转氨酶，但详尽的实验未能证明该反应的可逆性。γ,δ-二氧戊酸转氨酶合成δ-氨基乙酰丙酸的能力似乎远大于同一来源的δ-氨基乙酰丙酸合酶的能力。必须考虑γ,δ-二氧戊酸转氨酶在体内δ-氨基乙酰丙酸生物合成中发挥作用的可能性。
