Biosynthesis and degradation of saccharopine, an intermediate of lysine metabolism

Lysine–2-oxoglutarate reductase was prepared from ox liver and its characteristics were examined. Its activity was totally inhibited in the presence of NH₄Cl. Under conditions that inhibit saccharopine formation, and in the presence of NADP⁺, ox liver mitochondria were found to catalyse the hydrolysis of saccharopine to lysine and α-oxoglutarate. The enzyme involved was named saccharopine oxidoreductase. It was partially purified and separated from lysine–oxoglutarate reductase. Comparison of the properties of these two enzymes showed that saccharopine degradation was stimulated under conditions that inhibit its formation. The effect of pH, various cofactors and stability during incubation confirm that saccharopine biosynthesis from, and degradation to, lysine are catalysed by two distinct enzymes.