By using a sensitive fluorimetric assay of NAD+ glycohydrolase (EC 3.2.2.6), we showed that calf spleen cells are able to hydrolyse 1,N6-etheno-NAD+ given in the medium. The observed rates of substrate hydrolysis and product accumulation in the medium are equivalent. Moreover, the splenocytes are able to cleave the nicotinamide-ribose bond of a water-soluble polymer of NAD+, and their NAD+ glycohydrolase activity is fully inhibited by a high-molecular-weight Blue Dextran. Selective permeation of the cellular membrane digitonin revealed an intracellular pool of NAD+ glycohydrolase, which accounts for 25% of the total activity. We conclude that NAD+ glycohydrolase associated with the splenocytes has the characteristics of an ecto-enzyme.

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