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Malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+) () or NADP-malic enzyme (NADP-ME) is an enzyme that catalyzes the chemical reaction in the presence of a bivalent metal ion:〔 :(S)-malate + NADP+ pyruvate + CO2 + NADPH Thus, the two substrates of this enzyme are (S)-malate and NADP+, whereas its 3 products are pyruvate, CO2, and NADPH. Malate is oxidized to pyruvate and CO2, and NADP+ is reduced to NADPH. This enzyme belongs to the family of oxidoreductases, to be specific those acting on the CH-OH group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is (S)-malate:NADP+ oxidoreductase (oxaloacetate-decarboxylating). This enzyme participates in pyruvate metabolism and carbon fixation. NADP-malic enzyme is one of three decarboxylation enzymes used in the inorganic carbon concentrating mechanisms of C4 and CAM plants. The others are NAD-malic enzyme and PEP carboxykinase. Although often one of the three photosynthetic decarboxylases predominate, the simultaneous operation of all three is also shown to exist. ==Enzyme Structure== Based on crystallography data of homologous NADP-dependent malic enzymes of mammalian origin, a 3D model for C4 pathway NADP-ME in plants has been developed, identifying the key residues involved in substrate-binding or catalysis. Dinucleotide binding involves two glycine rich GXGXXG motifs, a hydrophobic groove involving at least six amino acid residues, and a negatively charged residue at the end of the βB-strand. The primary sequence of the first motif, 240GLGDLG245, is a consensus marker for phosphate binding, evidencing involvement with NADP binding, while the other glycine rich motif adopts a classical Rossman fold—also a typical marker for NADP cofactor binding. Mutagenesis experiments in maize NADP-ME have supported the current model.〔 Valine substitution for glycine in either motif region rendered the enzyme completely inactive while spectral analysis indicated no major changes from wild-type form. The data is suggestive of direct impairment at a key residue involved in binding or catalysis rather than an inter-domain residue influencing conformational stability. Additionally, a key arginine residue at site 237 has been shown to interact both with malate and NADP+ substrates, forming key favorable electrostatic interactions to the negatively charged carboxylic-acid and phosphate group respectively. Elucidation of whether the residue plays a role in substrate binding or substrate positioning for catalysis has yet to be determined. Lysine residue 255 has been implicated as a catalytic base for the enzymes reactivity; however, further studies are still required to conclusively establish its biochemical role.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+)」の詳細全文を読む スポンサード リンク
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