From a supplementary experiment with the cattle liver which contains much higher activity of the aldehyde oxidase than that of mouse and fowl livers, it was found that the nitrate reductase of the former was also inhibited similary by some purines as cases of the laters. Furthermore, the rate of inhibition by uric acid was lowered when the activity of the nitrate reductase had been activated by addition of acetaldehyde, increase of the amounts of enzyme employed or selection of liver of high activity. Concerning the nitrate reducing system of the purified preparation of cattle liver enzyme too, the purine inhibition coincided well with those of crude enzyme homogenate, though the former was not accompanied with the inherent hydrogen donators as well as some dehydrogenases which can couple with the nitrate reductase. A variation of ultraviolet absorption spectrum of the enzyme of high purity was brought about by addition of purines which suggest the combination of purines with enzyme protein.