Immunoreactive pancreatic colipase, lipase and phospholipase A2 in human plasma and urine from healthy individuals.

A radioimmunoassay for each of the human pancreatic proteins (colipase, lipase and phospholipase A2) is described. Determinations of the mean concentration of each protein in plasma and urine from healthy individuals were carried out with the radioimmunoassays. The values obtained in plasma were 0.5 nM (5.3 micrograms/l), 0.6 nM (32 micrograms/l) and 0.3 nM (4.3 micrograms/l) for colipase, lipase and phospholipase A2, respectively. In urine, the corresponding values were found to be 0.2 nM (2.4 micrograms/l), 0.09 nM (4.4 micrograms/l) and less than 0.017 nM (0.2 micrograms/l). No physical interaction between any of the three proteins and the lipid particles of plasma was demonstrated by centrifugation experiments or gel filtration. Gel filtration of plasma depleted of fat by centrifugation showed the proteins only in their monomeric form. The corresponding porcine proteins displayed a binding to antibodies against the human proteins, but with a lower affinity than the homologous interactions. The binding was weak but could differentiate between the porcine proforms and activated ones, i.e., procolipase and colipase87.