Glutaminase assay

Prusiner, S., and Milner, L. (1970). A rapid radioactive assay for glutamine synthetase, glutaminase, asparagines synthetase, and asparaginase. Anal. Biochem. 37, 429—438. 

This reaction requires catalytic amounts of nucleotide. Activity in the transferase assay generally gives rates several times higher than those obtained in the synthetase assays [Eqs. (1) and (2)] and for this reason is often used for measurement of glutamine synthetase, especially in relatively crude preparations. However caution should be exercised in the use of the transferase assay as a similar reactitm can also be catalyzed by some glutaminases and certain other amidases (Meister et al., 1955), although in these cases the reaction is not dependent on ADP, phosphate, or divalent metal cation. Levintow et al. (1955) demonstrated that the synthetase activity and the ADP phosphate divalent cation dependent transferase activity are functions of the same enzyme. 

In principle, any metabolic process that terminates in the production of ammonia or carbon dioxide can be similarly quantified in a continuous, automatic, incubation-quenching technique. Already some progress has been made with creatinine, another nitrogenous terminal metabolite, using an ammonia gas electrode [376], while glutaminase activity (arising from isoenzymes present in rat tissues and tumours) may be similarly determined [378]. Urea and tyrosine can be assayed [367] by using the appropriate decarboxylase and a carbon dioxide gas electrode. 

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