A Comparison of Glutamate Synthase Obtained from Maize Endosperms and Roots

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Abstract
Glutamate synthase (EC 2.6.1.53) was examined in developing endosperms and roots of maize. KCl is required for maximum activity in each tissue. The effect with KCl is seen with buffer strength of 25-100 mM in the assay. The optimum concentration for the enzyme from endosperm is 20 mM and for the enzyme from root tissue the saturating concentration is about 20 mM. In root material the enzyme is labile but activity can be restored if KCl is added to the assay. Divalent cations such as Mg2+ or Mn2+ also activate the enzyme to some extent. In each case NADH or NADPH can serve as reductant. The reaction is insensitive to .alpha.-aminooxyacetate, but is inhibited by glutamate, the glutamate analogs methionine sulfoximine and methionine sulfone and by the glutamine analogs azaserine and albizziin.