Studies on Glutamate Synthase from the Leaves of Higher Plants

Abstract

Ferredoxin-dependent glutamate synthase has been isolated and purified 170-fold from field bean (Vicia faba cv. Minor) leaves. The enzyme has a molecular weight of 145 000 and does not appear to contain non-haem iron. The K^m values of the enzyme for glutamine, 2-oxoglutarate, and ferredoxin are 330, 150, and 2 μM respectively. The specificity of the enzyme is extremely high and no substitutes for glutamine have been found. Azaserine is a potent inhibitor of glutamate synthase. Chloroplasts from four species of plants have been shown to carry out a light-dependent glutamate synthesis from glutamine. This reaction is also highly specific for glutamine and purified asparagine cannot substitute for glutamine.