Phosphorylations in rabbit liver in vivo.

1. Purified alkaline phosphatases from cow's milk and calf intestinal mucosa quantitatively convert TPN into DPN. DPN is not hydrolysed by either enzyme. 2. These results confirn that the third phosphate grouping of TPN is esterified (to ribose), since the action of both purified phosphatases is restricted to phospho mono-esters and amides. 3. Under the experimental conditions used, there was no measurable synthesis of TPN from DPN, either by enzymic transfer from phenyl phosphate by intestinal alkaline phosphatase or by non-enzymic transfer from phosphocreatine at pH 4-2. 4. By using alcohol dehydrogenase, followed by alkaline phosphatase, DPN and TPN can be estimated spectrophotometrically in the same solution.