COMPARATIVE STUDIES ON THE DEGRADATION OF GABA and TAURINE IN THE BRAIN

The degradation of taurine and GABA in mammalian brain was studied in vivo and in vitro. Small amounts of [35S]isethionate (10–20 pmol/g brain wet weight) and [35S]sulphate (about 2 pmol/g) were detected in mouse brain after intramuscular injection of [35S]taurine. Taurine also produced isethionate in rat brain homogenates (about 20 nmol/h/g protein) and subcellular fractions (about 40 nmol/h/g protein in synaptosomes and about 300 nmol/h/g in mitochondria), but the reaction was not stimulated either by external electrical pulses or by the addition of various cofactors (NAD and NADP in both oxidized and reduced forms, riboflavin, glutathione. pyridoxal‐5′‐phosphate, ATP) to the incubation medium. [14C]GABA was readily metabolized to [14C]succinate both in vivo and in vitro. Isethionate formation activity was concentrated in the mitochondrial fraction, as was also GABA‐T activity. Partially purified GABA‐T from calf brain also slightly catalysed the formation of [35S]isethionate (about 1.3 μmol/min/g protein) from [35S]taurine. It appears that the slight formation of isethionate from taurine is coupled to GABA‐T activity. The formation of isethionate from taurine is so small, that it apparently has no role in the control of the brain taurine pool.