Purification and immunological properties of human urinary kallikrein and prokallikrein.

Human urinary prokallikrein and kallikrein have been purified from the same source of urine simultaneously. The anti-kallikrein and anti-prokallikrein antibodies were raised in rabbits using the purified preparations. With respect to solid phase enzyme immunoassay (EIA), immunoaffinity column chromatography, and single radial immunodiffusion, reactivity of each antibody with kallikrein was distinctly different from that with prokallikrein. Kallikrein could be determined by anti-kallikrein antibody-immobilized EIA below 20 ng per ml, whereas prokallikrein was undetectable. Prokallikrein became detectable at higher concentrations, although it was less reactive than kallikrein. The anti-prokallikrein antibody-immobilized EIA detected both kallikrein and prokallikrein with the same sensitivity. However, the binding capacity for kallikrein was about one-third less than that for prokallikrein. The results show that kallikrein in human urine may be determined directly and selectively. Similar difference in reactivity was observed with immunoaffinity column chromatography and single radial immunodiffusion. The presence of 3-4 antigenic sites per molecule was indicated by quantitative precipitin reaction, and it is suggested from analysis of amino acid sequence of kallikrein by the method of Hopp and Woods that four hydrophilic regions exist in kallikrein molecule.