Significance of enzymatically catalyzed exchange reactions in chemotherapy.

1) 3-Acetyl pyridine has been found to be quite toxic when administered to mice. Simultaneous administration of nicotinamide or DPN protects against the toxicity of acetyl pyridine. Nicotinic acid and tryptophan do not protect animals from the lethal effects of the compound. 2) Nicotinamide inhibits the formation of the 3-acetyl pyridine analog of DPN from acetyl pyridine and DPN in mouse brain homogenates. Nicotinic acid has no inhibitory effect on analog synthesis. 3) Administration of acetyl pyridine results in a fourfold increase in the DPN level of the lever. No acetyl pyridine analog of DPN is found in the liver after injection of the antimetabolite. 4) Injection of acetyl pyridine into tumor mice results in the formation of the acetyl pyridine analog of DPN in the neoplastic tissues. A decrease in DPN concentration is associated with the analog synthesis. The DPN analog has been isolated from tumor tissue and identified. 5) The results are discussed with respect to the significance of enzymatically catalyzed exchange reactions in chemotherapy.