On the Optimum pH for Mold-Lecithase

Abstract

A_KAMATSU found by the estimation of the increased acidity and of the inorganic phosphoric acid that Taka-phosphatase (which is contained in Taka-diastase from Aspergillus oryzae) decomposes not only the synthetical glycerin-phosphoric acid, but also the glycerin-phosphoric acid which is a decomposed product from lecithin. One of the authors measured cholin, a decomposition product of lecithin by lecithase, and inorganic phosphoric acid, a decomposition product by phosphatase, and found that the estimation of cholin is a very convenient method for the study of lecithase. He observed that the degree of injurious effect of ultraviolet ray on the formation of inorganic phosphoric acid is different from that on the formation of cholin from lecithin by Taka-diastase, the former being the highest at pH 6.6. After Pincussen's reports, the injurious effect of ultraviolet ray upon the enzyme is the greatest at the optimum pH for the enzyme. Therefore, we suspected that the optimum pH for lecithase may be different from that of phosphatase.
In the following experiments, we have determined the optimum pH for lecithase by the measurement of cholin. For the estimation of cholin freed, we have used the following method: We added a small quantity of magnesium chloride solution and that of ammonia to the reaction mixture, filtered off the precipitates of magnesium hydroxide which includes the nondecomposing lecithin, added a iod-iodkali solution to the filtrate, separated the precipitate of cholin-periodide and solved in chloroform, and finally titrated freed iodine with N/100 thiosulphate solution. 1c.c. of N/100 Na₂S₂O₃=0.14mgr. of cholin.
To the lecithin-methylalcohol solution-0.5gr. of lecithin was solved in 5 c.c. of methylalcohol-40 c.c. of M/15 phosphate buffer solution and 20 c.c. of 5% Taka-diastase solution were added, and then the flask was filled to 100 c.c. with distilled water. After standing for a definite time at 36°-37°C, 10 c.c. of the reaction mixture was taken out, was filled to 11 c.c. with magnesium chloride solution and ammonia, and was filtered. Two c.c. of its filtrate was neutralised with hydrochloric acid, was added 0.2 c.c. of iod-iodkali solution, then cholin-periodide was collected by centrifuging, washed with the saturated NaCl solution at 0°C and was solved in chloroform. The iodine freed was titrated with N/100 Na₂S₂O₃ solution.
From the result of the experiment we see that the optimum pH-value for lecithase is near 7.0 (Table I.). Next, from the data we calculated the velocity-constant by using monomolecular equation and showed that the reaction velocity obeys the monomolecular reaction within 3 hours (Table II).