Roles of cysteine residues in the inhibition of human glutamate dehydrogenase by palmitoyl-CoA

Human glutamate dehydrogenase isozymes (hGDH1 andhGDH2) have been known to be inhibited by palmitoyl-CoAwith a high affinity. In this study, we have performed the cassettemutagenesis at six different Cys residues (Cys59, Cys93,Cys119, Cys201, Cys274, and Cys323) to identify palmitoyl-CoA binding sites within hGDH2. Four cysteine residuesat positions of C59, C93, C201, or C274 may be involved, atleast in part, in the inhibition of hGDH2 by palmitoyl-CoA.There was a biphasic relationship, depending on the levels ofpalmitoyl-CoA, between the binding of palmitoyl-CoA and theloss of enzyme activity during the inactivation process. The inhibitionof hGDH2 by palmitoyl-CoA was not affected by theallosteric inhibitor GTP. Multiple mutagenesis studies on thehGDH2 are in progress to identify the amino acid residuesfully responsible for the inhibition by palmitoyl-CoA.