In order to clarify the mechanism of the inhibitory effect of some additives on the enzymatic decomposition of 5'-inosinic acid (IMP)in fish muscle, the effect of sodium chloride and glycerine was examined on the 5'-nucleotidase and acid phosphatase in various fish muscle extracts.
The pH-activity curves observed for IMP-decomposition in fish muscle extract varied with the different fish species and their pattern could be well explained by the activity ratios of 5'-nucle-otidase to acid phosphatase. It was therefore confirmed that IMP is decomposed in fish muscle by the action of a 5'-nucleotidase and an acid phosphatase.
These enzymes were suppressed by addition of sodium chloride, in a competitive inhibitory manner. The apparent Ki values for 5'-nucleotidase and acid phosphatase of 8 species of fish examined, closely resembled each other, and were calculated to be 0.111-0.161M and 0.070-0.142M, respectively. It was also found that both enzymes were suppressed by addition of glycerine in the same manner. The apparent Ki values for 5'-nucleotidase and acid phosphatase of these fishes, regardless of difference of species of fish, were calculated to be 4.02-6.31M and 1.09-1.67M, respectively.