Changes in the Enzymatic Composition of Liver*

Rats made diabetic with alloxan have been shown to excrete less Nmethylnicotinamide than normal rats when given test doses of tryptophan (2). The present investigation was designed to determine the nature of the enzymatic alteration responsible for the difference between the two groups of animals. A deficiency in one or more of the enzymes needed for the conversion of tryptophan to nicotinic acid would obviously explain the results. No such deficiency was found, but, since not all of the steps in nicotinic acid biosynthesis have yet been described, only some of the enzymes could be assayed. An alternative explanation was suggested, however, by the finding of a very large increase in the concentration of an enzyme, picolinic carboxylase (3), which attacks the product of 3-hydroxyanthranilic