Isoelectric focusing patterns of urinary kallikrein in Dahl salt-hypertension susceptible and resistant rats.

Dahl salt-sensitive (S) rats which are susceptible to hypertension have lower urinary kallikrein excretion than salt-resistant (R) rats which are not susceptible. Some physicochemical characteristics of partially purified urinary kallikrein were compared between the S and R strains. The isoelectric focusing pattern of S kallikrein was shifted so that a higher proportion of enzyme was present in isoelectric forms that had higher pI values compared to the pattern for R kallikrein. This strain difference was unique to urinary kallikrein; it was not seen in kallikrein extracted from salivary glands. The isoelectric focusing pattern for R urinary kallikrein could be converted to an S-type pattern by treatment with neuraminidase, which suggests that the differing isoelectric focusing patterns arose from differences in the sialic acid content of the kallikrein. The S kallikrein was slightly more heat-labile than R kallikrein, which was also compatible with the lower sialic acid content of the S enzyme. Tests involving the active site of the enzyme (Km values, pH curves, and heat of activation) were identical for the S and R strains. It was concluded that the structural differences observed in urinary kallikrein between S and R strains were compatible with strain-specific posttranslational processing of the enzyme.