Identity of Phosphodiesterase and Phosphomonoesterase Activities with Nuclease P1 (a Nuclease from Penicillium citrinum)

Enzymatic properties of a purified Penicillium nuclease (designated as nuclease P1) were investigated. The enzyme activities for RNA, heat-denatured DNA, native DNA, 3′-AMP and 2′-AMP showed a great degree of similarity with respect to the following properties: a) Range of stable pH (5~8), b) temperature optima (at around 70°C), c) thermostability (about 50% inactivation at 67°C, pH 6.0 for 15 min, d) effect of metal ions and SH inhibitors, e) requirement of Zn2+, f) protection from the heat-inactivation by albumin and Zn2+, g) inactivation on standing in the cold and reactivation on heating, h) sensitivity to protease, and i) competitive relationship between substrates in the enzyme reaction. Moreover, the ratio of enzyme activities in several mutants of Penicillium citrinum was constant. From these results, together with constant ratio of the specific activities throughout purification, it is concluded that a single enzyme might be responsible for both phosphodiesterase and phosphomonoesterase functions.