Abstract
AbstractThe racemization of d‐aspartic acid to l‐aspartic acid has been successfully performed with a coupled enzyme system at 90 °C and a pH of about 4.0 by the assay of high‐performance liquid chromatography. This coupled enzymatic racemization is a successive two‐step reaction first induced by d‐amino acid oxidase and a subsequent coupled reaction by an aminotransferase clonezyme with the help of coenzyme pyridoxal 5′‐phosphate and cosubstrate l‐glutamate. Due to the very high temperature, part of the l‐aspartic acid is produced by the thermal effect. In fact the thermal racemization for aspartic acid can proceed from either d‐ or l‐aspartic acid via an intermediate fumaric acid and leads to the formation of d,l‐malic acid. The formation of α‐oxalacetic acid formed irreversibly from d‐aspartic acid with d‐amino acid oxidase can induce a side reaction to l‐alanine. The thermal effect may also be responsible for the production of d‐, and l‐alanine.
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