RETENTION OF P‐NITROPHENOL AND 4‐METHYLUMBELLIFERONE BY MARINE MACROALGAE AND IMPLICATIONS FOR MEASUREMENT OF ALKALINE PHOSPHATASE ACTIVITY1

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Abstract
During standardization of the methodology for estimating “cell‐bound” alkaline phosphatase activity (APA: phosphomonoesterase) inFucus spiralisL. (Phaeophyta), some of the nonphosphate moiety of the original phosphomonoester was found to be released to the medium subsequent to completion of the routine assays. This occurred with the two substrates generally employed in APA measurements: p‐nitrophenyl phosphate (pNPP) and 4‐methylumbelliferyl phosphate (MUP). Other marine macrophytes tested showed the same phenomenon. The conditions influencing retention were investigated to establish the simplest procedure for measuring APA. When using pNPP, the release of the product (p‐nitrophenol) after the assays was maximum when assays were run for longer than 20 min and at slightly acid pH or at high pNPP concentrations. When using MUP, the leakage of the product (4‐methylumbelliferone) after the assays was maximum when APA measurements were run for longer than 40 min and at neutral pH or at high MUP concentrations. The significance of the leakage of the nonphosphate moiety after APA assays is discussed.