The Enzymatic Oxidation of Cysteamine to Hypotaurine in the Presence of Sulfide

Abstract

Although the ability of animal tissues to oxidize thiols and organic disulfides to sulfinates and sulfonates has long been recognized, the enzymatic mechanism of this oxidation is obscure. For extensive literature on this field the reader is referred to recent reviews (1, 2). An enzyme capable of oxidizing cysteamine (RSH) to hypotaurine (R-S02H) and thiotaurine (R-SOaH), in the presence of inorganic forms of sulfur, however, has been recently detected in a number of animal tissues (3-6). The presence of elementary sulfur or sulfide was found essential for the activity of this enzyme, and it was postulated that thiocysteamine, i.e. the persulfide analogue of cysteamine (R-SSH), was formed and utilized as substrate (5, 7). Hypotaurine is the initial product of the reaction, whereas thiotaurine is produced by nonenzymatic transulfuration between hypotaurine and excess thiocysteamine or other polysulfides present (6). Furthermore it was observed that sulfide in small amount has an evident catalytic effect on the enzymatic reaction whereas at high concentrations it displays strong inhibition (6). This paper deals with the purification of this new enzyme, which we have extracted from horse kidney, and with a preliminary study of the mechanism of its action.