Pyrophosphoric acid (15 g/dl) and 8 g/dl of inosine or guanosine were dissolved in an acetate buffer (pH 4.0). To this was added E. coli JM109 strain having introduced therein each mutant acid phosphatase gene such that the concentration reached 100 mg/dl in terms of the dry cell weight. The reaction was conducted at 50° C. for 9 hours while maintaining the pH at 4.0, and the amount of 5′-inosinic acid or 5′-guanylic acid formed was measured. The results are shown in Table 17. The nucleoside phosphate ester formed was only a nucleoside-5′-phosphate ester, and the production of a nucleoside-2′-phosphate ester and a nucleoside-3′-phosphate ester as by-products was not observed at all. The reaction was also conducted at 30° C. for 12 hours using E. coli JM109/pEPI380 strain as a control. The results are also shown in Table 17.
