Human placental alkaline phosphatase electrophoretic alleles: quantitative studies

Human placental alkaline phosphatase (ALP) activity has been determined in specimens obtained from 562 Italian subjects. The mean activities of the three common homozygotes (Pl 2 = 4.70 +/- 0.24, Pl 1 = 4.09 +/- 0.08, and Pl 3 = 2.15 +/- 0.71 mumol of p-nitrophenol produced) were significantly different. The differences among the various allelic forms account for 10% of the total quantitative variation of the human placental alkaline phosphatase.