Distinctive interactions in the holoenzyme formation for two isoforms of glutamate decarboxylase

Reversal of Brain Injury-Induced Prefrontal Glutamic Acid Decarboxylase Expression and Working Memory Deficits by D1Receptor Antagonism

“…Although both enzymes are present in most GABA-containing neurons, GAD65 is a hydrophobic membrane-anchored form primarily found in axon terminals, whereas GAD67 is a soluble hydrophilic isoform distributed throughout the cell (Esclapez et al, 1994). Although both isoforms require the cofactor pyridoxal phosphate (PLP) for their enzymatic activity, GAD67 has a significantly higher binding affinity and lower dissociation constant for PLP than GAD65 (Chen et al, 2003). Therefore, most GAD67 exists as an active holoenzyme (bound with PLP), whereas GAD65 is primarily present as inactive apoenzymes (not bound with PLP) (Chen et al, 2003).…”

“…Although both isoforms require the cofactor pyridoxal phosphate (PLP) for their enzymatic activity, GAD67 has a significantly higher binding affinity and lower dissociation constant for PLP than GAD65 (Chen et al, 2003). Therefore, most GAD67 exists as an active holoenzyme (bound with PLP), whereas GAD65 is primarily present as inactive apoenzymes (not bound with PLP) (Chen et al, 2003). Furthermore, brain GABA levels are normal in GAD65 knock-out mice (Asada et al, 1996), whereas GABA levels are reduced in adult heterozygotes of GAD67 knock-out mice (Asada et al, 1997).…”

Characterisation of an autoreactive conformational epitope on GAD65 recognised by the human monoclonal antibody b78 using a combination of phage display, in vitro mutagenesis and molecular modelling

“…However, if such were the case, antibodies should react with one or the other, or with both isoforms of GAD, and not just GAD65. An explanation may be that the two isoforms bind PLP with quite different affinity [31], and circular dichroism data indicate that, upon gain or loss of binding to PLP, the GAD molecule undergoes a major conformational change [32], and this could affect antigenicity.…”

GAD isoforms exhibit distinct spatiotemporal expression patterns in the developing mouse lens: Correlation with Dlx2 and Dlx5

“…Conversely, GAD65 which is found mostly as an inactive apo-GAD (Martin et al, 2000;Battaglioli et al, 2003;Chen et al, 2003) and enzymatically active GAD44, regulated mostly at the translational level (Szabo et al, 1994) may provide an abundant, but more slowly mobilizable, pool of GAD during the extended process of primary fiber differentiation. This notion is supported by the observation that, despite the overall decreased GAD synthesis in P0 compared with E17.5 lens, the corresponding GABA level does not drop significantly.…”