Improved procedures for extraction of lysine 2‐oxoglutarate reductase/saccharopine dehydrogenase (LOR/SDH) enzyme fromPhaseolus vulgariscultivars

Lysine is one of the most limiting essential amino acid in food crops consumed by humans. Excess lysine is catabolised via saccharopine by two consecutive enzymes, lysine 2‐oxoglutarate reductase (LOR) and saccharopine dehydrogenase (SDH), linked on a single bifunctional polypeptide. The activities of LOR and SDH were shown to be similar in three distinct Phaseolus vulgaris cultivars. The addition of bovine serum albumin (BSA) to buffers resulted in different responses among the crude, 0–7.5%, and 7.5–15% polyethylene glycol (PEG) 8000 extracts. Different responses were also observed when the activities of LOR and SDH were tested after extraction in the presence of phosphatase inhibitors. The addition of lysine to the growth medium increased the activity of LOR, but not SDH. The results observed add new information on the regulation of LOR/SDH in a legume plant species.