Saccharopine, an Intermediate of the Aminoadipic Acid Pathway of Lysine Biosynthesis

The ϵ-amino group of lysine arises in yeast and Neurospora from glutamate in a unique transamination between α-aminoadipic δ-semialdehyde and glutamate involving the stable intermediate saccharopine. See PDF for Structure The enzyme catalyzing the terminal reaction, saccharopine dehydrogenase (ϵ-N-(L-glutaryl-2)-L-lysine:NAD oxidoreductase (L-lysine forming)) has been purified and shown to be a sulfhydryl enzyme having an approximate molecular weight of 49,000. Two distinct pH optima (approximately 10 and 7) exist for the forward and reverse directions of the enzyme-catalyzed reaction. The enzyme is stabilized in the presence of relatively high salt concentrations and has been shown to display a high degree of specificity with respect to the coenzyme and substrates. The Michaelis constants for lysine, oxoglutarate, and reduced nicotinamide adenine dinucleotide have been found to be 1.2 x 10-2 M, 4.4 x 10-4 M, and 4.6 x 10-5 M, respectively.