Influence of monoethanolamine on activity measurements of the isoenzymes of alkaline phosphatase.

In various countries (e. g. Federal Republic of Germany, Scandinavian countries) the activity measurement of alkaline phosphatase (orthophosphoric morioester phosphohydrolase, EC 3.1.3.1) with diethanolamine buffer is recommended as a standardised method (1, 2). This enzyme activity was hitherto measured chiefly in glycine buffer, but the activities measured in diethanolamine buffer are much higher, because the transphosphorylase reaction is measured in addition to the hydrolytic phosphatase (3, 4, 5). The reliability of this method of measuring the activity of alkaline phosphatase is, however, impaired by monoethanolamine, which may occur as an impurity in diethanolamine and acts as an inhibitor of alkaline phosphatase (6, 7). The aim of this study is to show the different influence of monoethanolamine on the activity of the various isoenzymes of alkaline phosphatase.