Transaminases stereochemistry

Figure 24.10. Stereochemistry of Proton Addition. In a transaminase active site, the addition of a proton from the lysine residue to the bottom face of the quinonoid intermediate determines the 1 configuration of the amino acid product. The conserved arginine residue interacts with the a-carboxylate group and helps establish the appropriate geometry of the quinonoid intermediate.

Tn amino acid production, we encounter an important problem in bio.synthesis—namely, stereochemical control. Because all amino acids except glycine are chiral, biosynthetic pathways must generate the correct isomer with high fidelity. In each of the 19 pathways for the generation ofchiral amino acids, the stereochemistry at the a-carbon atom is established by a transamination reaction that includes pyridoxal phosphate (PEP). Almost all the transaminases that catalyze these reactions descend from a common ancestor, illustrating once again that effective solutions to biochemical problems are retained throughout evolution. 

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