Mj. Bonete et al., NAD-GLUTAMATE DEHYDROGENASE FROM HALOBACTERIUM-HALOBIUM - INHIBITION AND ACTIVATION BY TCA INTERMEDIATES AND AMINO-ACIDS, Biochimica et biophysica acta (G). General subjects, 1289(1), 1996, pp. 14-24
A variety of metabolites have been found to elicit a form of inhibitio
n or activation on an NAD-specific glutamate dehydrogenase (NAD-GDH, E
C 1.4.1.2) from Halobacterium halobium,. The purified halophilic enzym
e was tested with several compounds known to be allosteric modifiers o
f mammalian glutamate dehydrogenases to determine their effects on enz
yme activity. GTP, ATP, ADP and AMP did not affect the enzyme, so thes
e effecters of bovine glutamate dehydrogenase do not play a role in th
e regulation of the halophilic enzyme. However, the halophilic enzyme
was subject to strong inhibition by TCA intermediates. When measuring
the initial rate of the reaction, the oxidative deamination of L-gluta
mate was inhibited by TCA metabolites such as: fumarate, oxalacetate,
succinate and malate; by substrate analogues such as: NADP(+), D-gluta
mate and glutarate; and by dicarboxylic compounds such as adipate. On
the other hand, all the amino acids tested were activators of this enz
yme, except the D-isomer of the substrate L-glutamate that acted as an
inhibitor. The relative effectiveness of each inhibitor or activator
(K-1 or K-2 values) was correlated with the dipole moment (mu), HOMO a
nd LUMO molecular orbital energies, optimal distance between two carbo
xyl groups, and hydrophobicity. Compounds with high dipole moment acte
d as good activators while compounds with low dipole moment were inhib
itors. We have also found that the best activators were amino acids wi
th no polar lateral chain.