抄録
A simple method of assaying phosphatase activity in soils from tidelands was developed. This method is based on the colorimetric estimation of phenolphthalein release from phenolphthalein phosphate. Both the colorization of the product and termination of the phosphatase reaction occur at the same time by adding an alkaline phosphate solution to the reaction mixture. Phenolphthalein has an absorption maximum around 550 nm with a higher molecular extinction coefficient than that of p-nitrophenol commonly used in a conventional phosphatase assay.
A blank value was obtained by adding the alkaline phosphate stop solution to the reaction mixture prior to the substrate addition. This value included the absorbance of the colorimetric substance derived from soils and any phenolphthalein spontaneously liberated from the substrate. Thus, the absorbance caused by the actual enzymatic reaction can be easily calculated by subtraction of the blank value from the total absorbance after the reaction.
In this assay, we employed a new soil unit, “packed volume”, which means the volume of tideland soil after centrifugation at 650 g. By measuring the compression ratio of the soil by centrifugation, the obtained specific activity of a packed soil can be easily converted to the phosphatase activity value in the tideland soil in the native state. Most phosphatase activity and ATP were present in the tideland sediment soil fraction. These results suggest that the present method is useful for the practical estimation of phosphatase activity of a bentotic environment and for comparison of the phosphatase activity among various tidelands.
