抄録
Phosphodiesterase I [EC 3. 1. 4. 1] was purified from normal human urine in a highly purified state free from phosphodiesterase II, RNase, DNase I, DNase II, and phosphatase by column chromatographies of DEAE-Toyopearl, butyl-Toyopearl, Affi-Gel blue, and Sephadex G-150. The molecular weight of the enzyme was 1.9×105 and the pH optimum around 9.0 with p-nitrophenyl deoxythymidine 5'-phosphate asthe substrate. The enzyme hydrolyzed the 3'-5' linkage of various dinucleoside monophosphates at approximately the same rate and the phosphodiester bonds of cyclic 3', 5'-mononucleotides to produce mononucleoside 5'-phos-phate. The enzyme also hydrolyzed ADP to 5'-AMP and P1, ATP to 5'-AMP and PP1, and NAD+ to 5'-AMP and NMN. The enzyme activity was abolished by removal of metal ions with EDTA, and the metal-free enzyme was reactivated on the addition of Zn2+. The enzyme activity was also abolished by some reducing agents and the inhibition was reversed by Zn2+. The metal-free enzyme was less stable than the native enzyme, and Zn2+ and Co2+ restored the stability of the metal-free enzyme to the level of the native enzyme. The enzyme degraded oligonucleo-tides and high molecular nucleotides stepwise from the 3'-termini to give 5'-mono-nucleotides. The enzyme hydrolyzed single-stranded DNA more preferentially than double-stranded DNA. The enzyme also nicked superhelical covalently closed circular φX174 DNA to yield first open circular DNA and then linear DNA.
