L-p-Bromotetramisole, a new reagent for use in measuring placental or intestinal isoenzymes of alkaline phosphatase in human serum.

L-p-Bromotetramisole is proposed as a new reagent for use in determining intestinal and (or) placental isoenzymes of alkaline phosphatase in human serum. Its main advantage over L-phenylalanine is its high discriminating potency at very low concentrations. For highest accuracy, the samples may even be "titrated" with the inhibitor. Analytical recoveries of intestinal and placental isoenzymes in serum are complete, and results correlate well with those by other methods. At the appropriate concentrations, L-p-bromotetramisole gives nearly identical results on a variety of sera, irrespective of the buffer used. Within-day CV's were 6.1 and 2.1 for 20% and 60% of the resistant isoenzyme activity, respectively. The day-to-day CV was 3.45 for a sample containing 53.3% of the resistant isoenzyme (n=15). The well-known increase in placental isoenzyme activity with time of gestation could be confirmed on 612 sera from pregnant women. The activities of the intestinal isoenzyme in sera from healty blood donors (n = 126) and hospitalized patients (n = 135) agree with previous findings obtained by the other techniques.