PH dependence of phosphatase activity in freshwater lakes.

Abstract

The pH dependence of phosphatase activity in lake water was investigated in eight Japanese lakes. Lakes Akanuma, Rurinuma and Bisyamonnuma were classified as acidotrophic and contained much SO42-, Cl-. Lakes Shibuike, Nagaike, Ichinuma were classified as dystrophic and contained much TOC, while Lakes Shinseiko and Ashinoko were both regarded as harmonic lakes. The phosphatase activities of Lakes Akanuma (pH 3.9), Rurinuma (pH 4.5), Shibuike (pH 4.5) and Nagaike (pH 5.6) were high under acidic conditions (pH 5-6), but low under alkaline conditions (>pH 8). The enzyme activity of Lake Bisyamonnuma (pH 5.7) was high under alkaline condition, while that of Lakes Ichinuma (pH 6.2), Shinseiko (pH 7.3) and Ashinoko (pH 7.3) was high under both acidic and alkaline conditions. Thus the phosphatase activity of these lakes was closely related to pH rather than components (SO42-, Cl-, TOC etc) dissolved in the water. The phosphatase collected in the water and that in homogenates of plankton from Lakes Shibuike and Shinseiko were fractionated by gel chromatography. Several phosphatases with various molecular weights (50, 000-270, 000) were observed under acidic condition in a plankton homogenate from Lake Shibuike. The molecular weight of the main dissolved phosphatase was 180, 000. In a water sample from Lake Shinseiko the molecular weight of the main soluble phosphatase with activity under alkaline conditions was 180, 000. This value corresponded to the molecular weight of the main phosphatase in the homogenate of plankton collected from the lake.