Enzymes of Nucleic Acid Metabolism from Wheat Seedlings

Abstract

A nuclease has been isolated from germinating wheat seedlings and purified over 830-fold. The purified preparation hydrolyzes denatured DNA, rRNA, and the 3′-phosphoester linkage of 3′-AMP at similar rates. The preparation exhibits no appreciable 5′-nucleotidase, phosphodiesterase, or phosphomonoesterase activity. The three enzyme activities have remained associated throughout a variety of purification procedures including chromatography on several ion-exchange resins, gel filtration, and polyacrylamide disc electrophoresis at pH 9.5 and 8.3. The ratios of the three activities remain essentially constant throughout all of these procedures. The three enzyme activities exhibit a great degree of similarity with respect to the following properties: (a) pH optima, (b) requirement for Zn++ and sulfhydryl compounds at pH 4.5, (c) rate of destruction of activity by sulfhydryl compounds at pH 8, (d) stability to storage, (e) effects of temperature and duration of heating, (f) reactivation on heating between 65° and 70°, (g) effect of N-bromosuccinimide, (h) effect of metal cations, and (i) effect of inhibitors and EDTA. It is concluded that the DNase, RNase, and 3′-nucleotidase activities in all probability reside in a single protein.