A direct assay for urinary kallikrein.

The first protein-binding assay is described for the direct determination of kallikrein in rat urine. Isolation of urinary kallikrein and preparation of its specific antibody have been previously described. Outlined here are the methods for 3H-labelling of kallikrein, for isolation of 3H-labelled immunoreactive enzyme, and for separation of free and antibody-bound kallikrein with the aid of double antibody. Assay and equilibrium conditions were characterized and a protocol is presented for the measurement of kallikrein concentration. The direct assay is sensitive, accurate and it correlates well (r = 0.81) with a functional assay. The assay may hold promise to determine catalytically active and inactive enzyme in urine, tissues and biological fluids.