Isocitrate dehydrogenase (IDH) [1,2] is an important enzyme of carbohydrate
metabolism which catalyzes the oxidative decarboxylation of isocitrate into
α-ketoglutarate. IDH is either dependent on NAD+ (EC 1.1.1.41) or on NADP+
(EC 1.1.1.42). In eukaryotes there are at least three isozymes of IDH: two are
located in the mitochondrial matrix (one NAD+-dependent, the other NADP+-dependent), while the third one (also NADP+-dependent) is cytoplasmic. In
Escherichia coli the activity of a NADP+-dependent form of the enzyme is
controlled by the phosphorylation of a serine residue; the phosphorylated form
of IDH is completely inactivated.
3-isopropylmalate dehydrogenase (EC 1.1.1.85) (IMDH) [3,4] catalyzes the third
step in the biosynthesis of leucine in bacteria and fungi, the oxidative
decarboxylation of 3-isopropylmalate into 2-oxo-4-methylvalerate.
Tartrate dehydrogenase (EC 1.1.1.93) [5] catalyzes the reduction of tartrate
to oxaloglycolate.
These enzymes are evolutionary related [1,3,4,5]. The best conserved region of
these enzymes is a glycine-rich stretch of residues located in the C-terminal
section. We have used this region as a signature pattern.
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