A sensitive colorimetric assay for human urinary kallikrein.

L-Prolyl-L-phenylalanyl-L-arginine-alpha-naphthylester (Pro-Phe-Arg-NE) was synthesized as a new substrate for use in the assay of kallikreins. An assay was developed based on the colorimetric determination of alpha-naphthol released by the enzyme reaction. With Pro-Phe-Arg--NE as substrate, the minimum detectable concentration of human urinary kallikrein, was about 0.001 KU. Thus use of Pro-Phe-Arg-NE provides a highly sensitive method for detection of human urinary kallikrein. Kallikrein could be determined with a 25-microliter sample of human urine. Zymograms of human urinary kallikrein were prepared using Pro-Phe-Arg-NE as substrate. Six bands were separated by polyacrylamide disc gel isoelectrophoresis.