Urinary tissue plasminogen activator in renal disease.

Whereas plasminogen activator of the tissue-type (t-PA) is present in extracts of kidney parenchyma, only small amounts of the enzyme can be detected in normal urine where the major plasminogen activator is of the urokinase-type (u-PA). These observations suggest the existence of physiological or anatomical barriers that effectively confine t-PA to renal tissue and exclude it from the urine. We examined the notion that disease might breach these barriers and so lead to the appearance of abnormal amounts of t-PA in the urine. Under the conditions of the simple fibrinolytic assay that we have developed, urine samples from 30 normal subjects did not contain detectable amounts of t-PA whereas we were able to demonstrate t-PA in samples from 43 of 65 patients with various forms of renal disease. When positive, therefore, tests for the presence of t-PA in human urine provide evidence for renal disease that may not otherwise be apparent.

The Erythrina protease inhibitor: interactions with tissue plasminogen activator.

The Kunitz-type trypsin and tissue plasminogen activator (t-PA)-inhibitor from Erythrina caffra seeds was cleaved by trypsin at low pH to yield a disulphide linked two-chain molecule with reduced hydrophobicity. This change was used to separate cleaved from native inhibitor by phenyl-Sepharose chromatography. The inhibitor was not cleaved by t-PA. Trypsin, but not t-PA, catalysed resynthesis of the cleaved bond. Although the cleaved protein retained inhibitory activity for both trypsin and t-PA, 6-10 times higher concentrations were required for equivalent inhibition. Removal of the active site arginine (Arg63) from the cleaved inhibitor by digestion with carboxypeptidase B resulted in a further loss of inhibitory activity towards both proteases. The activity of the inhibitor could also be decreased by modification of one susceptible arginine residue with peptidyl arginine deiminase. These results suggest that the trypsin-reactive site of the Erythrina inhibitor is also involved in the interaction between the inhibitor and t-PA.