Glutamic-aspartic transaminase of Dolichos lablab: participation by iron as a cofactor

Abstract

Glutamic acid-aspartic acid transaminase has been purified about 23-fold from a plant source, beans of Dolichos lablab. Fe has been shown to participate as a cofactor with pyridoxal phosphate in the enzymic transamination. Fe estimations were carried out during the various stages of purification and the ratio of Fe to specific activity was found to be constant. The participation of Fe has been demonstrated by studying its influence on the formation of oxaloacetic acid, [alpha]-oxoglutaric acid and aspartic acid respectively when the reaction was studied in both directions. The optimum pH of the enzyme was found to be between 8.2 and 8.5. Thyroxine inhibited the transaminase activity. Thyroxine incubated with Fe before addition to the enzyme system inhibited the activity to a considerably less extent than when only thyroxine was added.