Oxidation of hypotaurine in vitro by mouse liver and brain tissues

The oxidation of hypotaurine to taurine, a reaction so far very poorly characterized in mammals, exhibited characteristic properties of an enzyme-catalyzed reaction in the mouse liver and brain. It was pH- and temperature-dependent and obeyed Michaelis-Menten kinetics when assayed with tissue homogenates using [35S]hypotaurine as substrate. Most of the oxidation activity was recovered in the brain in the soluble fraction whereas in the liver the activity was more evenly distributed among the subcellular fractions. The oxidation was more susceptible to heavy metals and alkylating agents in the brain than in the liver. The activity was higher in both organs in developing than in adult mice. The optimum incubation conditions for oxidation by liver homogenates included pH 9.0, oxygenation of the reaction mixture and the presence of 50 mumol/l Cu2+ and 50 mmol/l NAD+. The specificity of the enzyme(s) for hypotaurine still remains open.