Components of the kallikrein-kinin system in urine

The excretion of kallikrein in urine varies, but the pathophysiologic implications are not clear. To help clarify the role of the urinary kallikrein-kinin system, we have begun to define components of the system as they occur in urine. To minimize artifacts which may arise through extensive purification procedures, we studied urinary protein concentrates prepared by ultrafiltration. The concentrates were separated by chromatography on Sephacryl. Urine contains abundant kininase activity, but in strongly inhibited forms. Kininase II is separable into at least two forms. Another major kininase can hydrolyze benzoyl-Pro-Phe-Arg and is inhibited by arginine but not by BPP9a or SQ 14,225. Its molecular weight is approximately 63,000. A third kininase, not inhibited by BPP9a, is excluded from Sephacryl. Human urine appears to contain only one kallikrein-like enzyme (MW 45,000). In addition, urine contains a protein (MW approximately 80,000) which reacts with trypsin to release bradykinin and which inhibits the hydrolysis of Pro-Phe-Arg-[3H]anilide by urinary kallikrein. Thus, in addition to kallikrein and kinins, urine contains kininogen and at least three kininase enzymes. Urinary ultrafiltrate contains an inhibitory substance (approximately MW 400).