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Controlling reaction specificity in pyridoxal phosphate enzymes

Michael D. Toney
Biochimica et biophysica acta 2011 v.1814 no.11 pp. 1407-1418
nitrogen metabolism, organisms, transamination, pyridoxal phosphate, enzymes, acids, decarboxylation, amino acids, active sites, pyridoxal, enzymology
Pyridoxal 5′-phosphate enzymes are ubiquitous in the nitrogen metabolism of all organisms. They catalyze a wide variety of reactions including racemization, transamination, decarboxylation, elimination, retro-aldol cleavage, Claisen condensation, and others on substrates containing an amino group, most commonly α-amino acids. The wide variety of reactions catalyzed by PLP enzymes is enabled by the ability of the covalent aldimine intermediate formed between substrate and PLP to stabilize carbanionic intermediates at Cα of the substrate. This review attempts to summarize the mechanisms by which reaction specificity can be achieved in PLP enzymes by focusing on three aspects of these reactions: stereoelectronic effects, protonation state of the external aldimine intermediate, and interaction of the carbanionic intermediate with the protein side chains present in the active site. This article is part of a Special Issue entitled: Pyridoxal Phosphate Enzymology.