A simple and sensitive method for determination of human urinary kallikrein activity (kininogenase activity), using human low molecular weight kininogen.

Human low molecular weight kininogen was partially purified and applied to the measurement of human glandular kallikrein as a substrate. The prepared human low molecular weight kininogen did not contain any significant amounts of kinin generating or destroying enzymes. When ethanol was added to the assay tube to stop the enzyme reaction, the substrate was almost completely removed from the incubation solution. Moreover, less than 1.25% ethanol had no effect on the kinin radioimmunoassay. These data suggest that the measurement of generated kinin can be done directly after the addition of ethanol. In this assay system, control tubes were unnecessary since the small volume of the urine samples (0.5 to 2.0 nl) contained negligible amounts of endogenous kinin. In a comparison of the availability as a substrate for human urinary kallikrein among human, dog and bovine low molecular weight kininogens, the enzyme activity was 5 or 100 times as high in the human substrate as in the dog and bovine substrates, suggesting that a human substrate is best for the human enzyme. A significant correlation was found between our previous method using bovine substrate and this method for human urinary kallikrein activity. In both methods, urinary kallikrein excretions were significantly lower in patients with essential hypertension and higher in those with primary aldosteronism, respectively. This simple, specific and sensitive kininogenase assay system seems to be very useful for investigating the physiological or pathophysiological role of the renal kallikrein-kinin system in hypertensive and renal diseases.