Glutaminase catalyzes reaction of Glutamate to GABA

• Using NMR spectroscopy, we show that Glutaminase reaction involves two steps.
• In the first step, Glutaminase catalyzes the conversion of Glutamine to Glutamate.
• In the second step, Glutaminase catalyzes the Glutamate formed to GABA.
• Rate of conversion of first step is ∼91 times faster than the second step.

Here, for the first time, we report an NMR spectroscopy study of l-Glutamine (Gln) conversion by Glutaminase (Glnase), which shows that the reaction involves two distinct steps. In the first step, Glnase rapidly hydrolyzes Gln to Glutamate (Glu) (∼16.87 μmol of Gln/min/mg of Glnase) and in the second step, Glu generated in the first step is decarboxylated into gamma-amino butyric acid (GABA) with a much slower rate (∼0.185 μmol/min/mg). When Glnase was added to the sample containing l-Glu alone, it was also converted to GABA, at a similar rate as in the second step mentioned above. The rate of Glu decarboxylation into GABA by Glnase is about an order of magnitude lower than that by commonly known enzyme, Glutamate decarboxylase. Potential impact of these findings, on the mechanistic aspects of Gln–Glu shuttle in neuroscience and glutaminolysis in tumors, is discussed.