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A Comparison of Glutamate Synthase Obtained from Maize Endosperms and Roots ¹

^a Department of Biology, McMaster University, Hamilton, Ontario L8S 4K1 Canada

Glutamate synthase (EC 2.6.1.53) has been 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 to 100 millimolar in the assay. The optimum concentration for the enzyme from endosperm is 20 millimolar and for the enzyme from root tissue the saturating concentration is about 20 millimolar. 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 -aminooxyacetate, but is inhibited by glutamate, the glutamate analogs methionine sulfoximine and methionine sulfone, and by the glutamine analogs azaserine and albizziin.

¹ This work was supported by grants from the National Research Council of Canada (A-2818) and Agriculture Canada (AC-7040).