QUANTIFICATION OF THE N-TERMINAL PROPEPTIDE OF HUMAN PROCOLLAGEN TYPE-I (PINP) - COMPARISON OF ELISA AND RIA WITH RESPECT TO DIFFERENT MOLECULAR-FORMS

This paper compares the results of procollagen type I N-terminal prope ptide (PINP) quantification by radioimmunoassay (RIA) and enzyme linke d immunosorbent assay (ELISA). PINP in serum from a patient with uremi c hyperparathyroidism was measured in RIA and ELISA to 20 mu g l(-1) a nd 116 mu g l(-1) and the corresponding concentrations in dialysis flu id were 94.5 mu g l(-1) and 140 mu g l(-1), respectively. PINP antigen appears in two distinct peaks following size chromatography and the t wo peak fractions display immunological identity and identical M-r's ( 27 kDa; SDS-PAGE). Analysis of fractions from size separated amniotic fluid, serum and dialysis fluid demonstrated that the RIA failed to me asure the low molecular weight form of PINP. However, the anti-PINP su pplied with the RIA-kit and the anti-PINP applied in the ELISA reacted equally well with both molecular forms of PINP when analysed in a dir ect ELISA. It is concluded that the major difference in the ELISA and RIA results is due to assay efficacy with respect to the low molecular weight form of PINP. (C) 1998 Elsevier Science B.V.