Concomitant synthesis and degradation of glutamine in isolated rabbit kidney tubules

When rabbit kidney tubules were incubated with 1 mM [1-14C]glutamine as substrate, a release of 14CO2 together with a net production of glutamine were observed. That glutamine utilization was masked by higher rates of concomitant glutamine synthesis was demonstrated by: (i) inhibiting glutamine synthesis; and (ii) measuring the specific radioactivity of [1-14C]glutamine which fell during incubation.