Fluorimetric assay of phosphate-activated glutaminase

A fluorimetric assay for the estimation of phosphate-activated glutaminase is presented. The liberated glutamate is separated from glutamine using a Dowex centrifugation technique allowing multiple samples to be rapidly analyzed. Glutamate is estimated fluorimetrically by reaction with o-phthaldialdehyde. Parameters for the assay were worker out based upon characterization of human frontal cortex glutaminase. High phosphate-activated glutaminase was found in cultured human skin fibroblasts and amniotic fluid cells and rat frontal cortex and striatum. Human caudate nucleus and frontal cortex activity was variable, but related in an exponential manner. Human and rat liver activity was markedly lower than brain activity.