GLUTAMATE-DEHYDROGENASE OF SPHAGNUM

Glutamate dehydrogenase (GDH) of S. fallax was purified 2000-fold to a pparent homogeneity. As estimated by gel filtration and SDS-PAGE, a na tive molecular weight of M-r 210 000 anda subunit molecular weight of M-r 52000 were determined, indicating that the enzyme is tetrameric wi th subunits of identical molecular weights. Isoforms could not be dete cted. Purified GDH displayed pH-optima of 8.6 with NAD(P)H and 7.7 wit h NAD(+) and a high K-m for ammonium of 28 and 41 mM with NADH and NAD PH as coenzymes, respectively. The enzyme is located in the mitochondr ia. The occurrence of GDH activity in the cytosolic fraction was addre ssed to organelle breakage. Enhanced ammonium concentrations and a red uced carbon supply caused a substantial increase in GDH activity, Labe lling studies with [N-15]ammonium and [N-15]glutamate were consistent with the role of the enzyme in the oxidative deamination of glutamate. (C) 1997 Elsevier Science Ltd. All rights reserved.