Hypotaurine Oxidation by Mouse Tissues

Abstract

There are possibly two main biosynthesis pathways of taurine in mammalian tissues. Taurine is formed either from cysteine via cysteine sulphinic acid and hypotaurine intermediates (Jacobsen and Smith, 1968) or from phosphopantothenylcysteine via cysteamine and hypotaurine (Cavallini et al., 1976; Scandurra et al., 1977). The key intermediate in both metabolic routes is hypotaurine, 2-amino-ethanesulphinic acid. The oxidation of hypotaurine to taurine has not yet been adequately demonstrated. Cavallini et al. (1954) were unable to detect any oxidation, whereas Sumizu (1962) reported that liver homogenates could oxidize hypotaurine in the presence of NAD⁺. Later, Fiori and Costa (1969) were unable to confirm his observation, but Oja et al. (1973) found some activity in tissues of developing rats. Fiori and Costa even suggested that hypotaurine is oxidized by the trace amounts of H₂O₂ produced by cellular metabolism. Recently, Di Giorgio et al. (1977; 1978) have demonstrated hypotaurine oxidation in the retinal subcellular fractions of different animals using the method of Oja et al. (1973). The properties of the oxidation reaction have not, however, been investigated in detail, even if the hypotaurine: NAD⁺ oxidoreductase (EC 1.8.1.3) enzyme has been prematurely listed and assigned a number on the basis of the poorly controlled short communication of Sumizu (1962). In particular, the true enzymatic nature of hypotaurine oxidation has never been satisfactorily confirmed.