Ad. Uttaro et al., A family of highly conserved glycosomal 2-hydroxyacid dehydrogenases from Phytomonas sp., J BIOL CHEM, 275(41), 2000, pp. 31833-31837
Phytomonas sp. contains two malate dehydrogenase isoforms, a mitochondrial
isoenzyme with a high specificity for oxaloacetate and a glycosomal isozyme
that acts on a broad range of substrates (Uttaro, A. D., and Opperdoes, F.
R, (1997) Mol. Biochem. Parasitol. 89, 51-59). Here, we show that the low s
pecificity of the latter isoenzyme is the result of a number of recent gene
duplications that gave rise to a family of glycosomal 2-hydroxyacid dehydr
ogenase genes. Two of these genes were cloned, sequenced, and overexpressed
in Escherichia coli. Although both gene products have 322 amino acids, sha
re 90.4% identical residues, and have a similar hydrophobicity profile and
net charge, their kinetic properties were strikingly different. One isoform
behaved as a real malate dehydrogenase with a high specificity for oxaloac
etate, whereas the other showed no activity with oxaloacetate but was able
to reduce other oxoacids, such as phenyl pyruvate, 2-oxoisocaproate, 2-oxov
alerate, 2-oxobutyrate, 2-oxo-4-methiolbutyrate, and pyruvate.