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Monoesterase of dialyzed afternoon urine was strong enough to hydrolyze monophenolphosphate completely within one hour, when 2 ml of it was incubated with 1 ml of M/100 the substrate solution at pH 5. The dialyzed urine contained no pyrophosphatase and esterpyrophosphatase. In this experiment urine monoesterase was used, since the preparation of a strong liver monoesterase solution free from pyrophosphatase and esterpyrophosphatase was laborious. pH optima of liver esterpyrophosphatase were found at 4.0 and 8.0. At those pH was esterpyrophosphatase neither inhibited nor activated by Mg^<++> and Ca^<++>. As indicated above the presence in liver of two isodynamic enzymes was probable. An attempt was made to separate them from each other and the alkaline esterpyrophosphatase was obtained by the following procedures; N/10 HCl was added to the heated and dialyzed liver autolysate mentioned above to adjust the pH to 3.0, the solution was heated again at 75℃ for 10 minutes and neutralized to pH 5.8 (using pH meter) by adding of N/10 NaOH. The turbid solution was stored in ice-box for 16 hours. The sedimented precipitate was centrifuged and suspended in water, volume of which was twenty fifth of original solution. This suspension was capable of splitting pyrophosphate bridge of DPP solely in alkaline reaction (optimum pH 8.0). Isolation of esterpyrophosphatase which would be active only on the acid side was impossible.

It has been reported by Kurata of this department that diphenolpyrophosphate (abbreviated as DPP) was hydrolysed by activated pyrophosphatase into 2 moles of monophenolphosphate. The present experiment has shown that DPP can be splitted at the pyrophosphate linkage by an enzyme solution which contains no pyrophosphatase. Such a solution was prepared as follows: The dialyzed autolysate of hog liver was acidified to pH 5 by addition of N/2 acetic acid and centrifuged. The supernatant was neutralized with N/10 NaOH to pH 9.0, heated at 65℃ for 10 minutes and dialyzed. This enzyme solution was inactive upon monophenolphosphate and pyrophosphate, but DPP was hydrolysed to monophenolphosphate, the presence of which was certified by following procedure. The incubated reaction mixture, in which any production of phenol or inorganic phosphate was heated at 100℃ for 5 minutes in order to inactivate the enzyme, and liver phosphomonoesterase (optimum pH 3.2) was added. Thereafter phenol and inorganic phosphate were liberated in equivalent amount. That acid monoesterase solution, which was free from pyrophosphatase and inactive upon DPP, was prepared by treating hog liver autolysate acidified with acetic acid and dialysing the centrifuged supernatant. Phosphodiesterase III (Habe) and IV (kidney) liberated no phenol from DPP. There was, therefore, an enzyme in the heated enzyme solution mentioned above which splits DPP into monophenolphosphate. This enzyme is named esterpyrophosphatase. Quantitative estimation of esterpyrophosphatase activity calls for the measurement of monoplenolphosphate which has been produced as the result of DPP hydrolysis. Since it is impossible to measure the liberated monophenolphosphate directly, an indirect method was carried out by measuring phenol which would be liberated after successive action of urine phosphomonoesterase (optimum pH 5.0).