Taurine in Infant Nutrition

Taurine (fig. 1) is one of the most abundant amino acids in the body (1), with the largest pool present in muscle. In mammals, taurine and inorganic sulfate are the major end products of methionine metabolism (fig. 2). Despite the fact that taurine is both ubiquitous and abundant, it takes part in few known biochemical reactions. Considerable taurine is conjugated with bile acids in liver (1), but other biochemical reactions take place to a very limited extent, if at all (2). Although there are numerous proposals for alternative pathways for the biosynthesis of taurine (cf. 2), the enzyme immediately responsible for its synthesis in physiologically significant amounts is cysteinesulfinic acid decarboxylase. There are large differences amongst species in the in vitro activity of this enzyme, as there are in the concentration of taurine itself (1). For example, the activity of cysteinesulfinic acid decarboxylase, as measured in our laboratory, is 1000-fold higher in adult rat liver than in adult human liver (table 1).