Malic enzyme, conserved site <p>Malic enzymes (malate oxidoreductases) catalyse the oxidative decarboxylation of malate to form pyruvate [<cite idref="PUB00001542"/>], a reaction important in a number of metabolic pathways - e.g. carbon dioxide released from the reaction may be used in sugar production during the Calvin cycle of photosynthesis [<cite idref="PUB00002876"/>]. There are 3 forms of the enzyme [<cite idref="PUB00002681"/>]: an NAD-dependent form that decarboxylates oxaloacetate; an NAD-dependent form that does not decarboxylate oxalo-acetate; and an NADPH-dependent form [<cite idref="PUB00002876"/>]. Other proteins known to be similar to malic enzymes are the <taxon tax_id="562">Escherichia coli</taxon> scfA protein; an enzyme from <taxon tax_id="4577">Zea mays</taxon> (Maize), formerly thought to be cinnamyl-alcohol dehydrogenase [<cite idref="PUB00004541"/>]; and the hypothetical <taxon tax_id="4932">Saccharomyces cerevisiae</taxon> protein YKL029c.</p><p>Studies on the duck liver malic enzyme reveals that it can be alkylated by bromopyruvate, resulting in the loss of oxidative decarboxylation and the subsequent enhancement of pyruvate reductase activity [<cite idref="PUB00000616"/>]. The alkylated form is able to bind NADPH but not L-malate, indicating impaired substrate-or divalent metal ion-binding in the active site [<cite idref="PUB00000616"/>]. Sequence analysis has highlighted a cysteine residue as the point of alkylation, suggesting that it may play an important role in the activity of the enzyme [<cite idref="PUB00000616"/>], although it is absent in the sequences from some species.</p><p>There are three well conserved regions in the enzyme sequences. Two of them seem to be involved in the binding NAD or NADP. This entry represents the third domain, located in the central part of the enzymes, its function is not yet known.</p>