Influence of inorganic phosphate on the activity determination of isoenzymes of alkaline phosphatase in various buffer systems.

The inhibitory effect of inorganic phosphate on the activity determination of isoenzymes of alkaline phosphatase (AP) in diethanolamine (DEA), glycine and 2-amino-2-methyl-1,3-propandiol (AMPD) buffer was studied. This effect depends on the buffer used and isoenzyme investigated. Especially the placental isoenzyme is inhibited; the inhibitory effect in DEA buffer is stronger than in the other buffers used. The requirement of purity for 4-nitrophenylphosphate with respect to its content of inorganic phosphate and conclusions for using control sera enriched with AP isoenzymes are discussed.