A simple radioassay for human urinary kallikrein

Direct determination of kallikrein by high-performance liquid chromatography

A direct and specific identification of porcine pancreatic kallikrein by high-performance hydrophobic chromatography is proposed; the minimum amount which can be injected is 2.5 U. An application to the quantitative determination of the enzyme by high-performance size-exclusion chromatography is reported; the method is precise with a mean coefficient of variation of 2.8% and the minimum amount which can be injected is 0.02 U of kallikrein. The results obtained with determinations in real biological samples (porcine pancreatic powder and human urine) are reported. The method is based on direct and specific chromatographic signals and does not destroy the biological activity of this enzyme.

Radiolabelled substrates for angiotensin converting enzyme

Six [3H]benzoyl-tripeptides were prepared and tested as substrates for angiotensin converting enzyme. Each was prepared first as its [4-iodo]-benzoyl-analog, and an atom of 3H per molecule was introduced by catalytic dehalogenation in 3H2-gas. Kinetic parameters were measured at 37 degrees C using as buffer 0.05 M Hepes, pH 8.0 containing 0.1 M NaCl and 0.6 M Na2SO4. When the substrates were used at concentrations far below their respective Km values, fractional rates of substrate utilization per unit time for constant enzyme concentration were direct function of respective second order rate constants (Kc/Km). Although absolute values of Kc/Km differed for human enzyme as opposed to rabbit enzyme, relative values of Kc/Km were virtually identical. Similarly, relative rates of substrates utilization during passage through lungs of anesthetized rats were similar to relative values of Kc/Km measured in vitro. Thus, there is now a range of ACE substrates usable, in vitro and in vivo, under conditions of first order enzyme kinetics, conditions under which values of V/Km and Ki can be measured directly.