The reduction of cozymase by sodium borohydride.

Cozymase (diphosphopyridine nucleotide, DPN) has been assayed by a variety of biochemical and chemical methods (1). Among the simplest procedures has been the determination of the light absorption of reduced DPN at 340 rnp after reduction by sodium hydrosulfite. Since special precautions are required to remove completely the excess reducing agent which absorbs in this region, it appeared advantageous to tind another reducing agent which could be employed for the same purpose with greater ease. A study of the action of sodium borohydride (NaBH4) on DPN revealed that it filled the necessary requirements. The main advantage of this new reagent lies in its absence of light absorption at 340 rnlr. Spectrophotometric measurement of DPN reduced by NaBHd may therefore be made without removal of excess reagent. The assay procedure together with some observations on the properties of the reduction product will be described in this communication.