|
type |
Journal Article |
authors |
Varticovski, L.; Kushner, J. P.; Burnham, B. F. |
title |
Biosynthesis of porphyrin precursors. Purification and characterization of mammalian L-alanine:gamma,delta-dioxovaleric acid aminotransferase |
journal |
J Biol Chem |
Activity |
2.6.1.43 |
ui |
80160007 |
year |
(1980) |
volume |
255 |
number |
8 |
pages |
3742-7. |
| |
keywords |
Animal |
abstract |
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. |
last changed |
2002/11/12 16:17 |
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