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1. An enzyme solely localized in the nuclear fraction of rat liver was found to convert 3-hydroxyanthranilic acid into a red product that was isolated and crystallized from the reaction mixture. The product was identified as cinnabarinic acid (2-amino-3-oxo-3H-phenoxazine-1,9-dicarboxylic acid) by comparing its properties with synthetic cinnabarinic acid. 2. The enzyme had optimum pH at 7.2. Heavy-metal ions like Ag(+), Hg(2+), MoO(4) (2-), Fe(2+) and Cu(2+) were inhibitory; Mn(2+) activated the reaction to a considerable extent. 3. The reaction was inhibited by mercaptoethanol, GSH and cysteine, and activated by p-hydroxymercuribenzoate and sodium arsenite, which may suggest the involvement of disulphide groups in the reaction.

1. The specific NAD-glycohydrolase activity is increased 70 and 50% over the normal in lung and liver tissues respectively of tuberculous mice. 2. Concomitant with the increase in the NAD-glycohydrolase activity, the NAD-isonicotinic acid hydrazide-exchange activity also is increased in infection. The isonicotinic acid hydrazide analogue of NAD formed by the lung enzyme from tuberculous mice has been isolated and identified. 3. The increased NAD-glycohydrolase activity in infection has been shown to be of host-tissue origin and not due to the activation of the bacterial enzyme on growth of the organism in vivo. 4. In addition to NAD, NMN and NADP also participate in the exchange reaction with isonicotinic acid hydrazide catalysed by NAD glycohydrolase. The interference of the drug at the nucleotide level of metabolism is therefore suggested.