Kallikrein inhibitors in rat plasma

Area of Science:

• Biochemistry
• Enzymology
• Proteomics

Background:

• Plasma kallikreins are crucial proteases involved in various physiological processes.
• The presence and characterization of kallikrein inhibitors in biological fluids are important for understanding protease regulation.
• Previous studies have indicated the existence of kallikrein inhibitors in plasma, but their specific nature and properties require further elucidation.

Purpose of the Study:

• To determine the kallikrein inhibitor content in human and animal plasma.
• To isolate and characterize novel inhibitors of glandular kallikreins from rat plasma.
• To differentiate these inhibitors from known protease inhibitors like alpha1-antitrypsin.

Main Methods:

• Enzyme inhibition assays using glandular kallikreins and substrates like Nalpha-benzoyl-L-arginine ethyl ester (BAEE).
• Biochemical separation techniques including Sephadex G-200 gel filtration and Ampholine focusing.
• Enzyme activity assays in dog vasodilator models.
• Determination of inhibitor properties such as optimal pH, thermal stability, isoelectric point, and molecular weight.

Main Results:

• Rat plasma exhibited the highest kallikrein inhibitory activity, inactivating 230-700 kallikrein units (KU) per ml.
• Two distinct inhibitory fractions were isolated from rat plasma: one associated with alpha2-macroglobulin and another eluted prior to albumin.
• The novel inhibitor demonstrated broad specificity, inhibiting glandular and plasma kallikreins, trypsin, and alpha-chymotrypsin, with an optimal pH of 7.5-8 and a molecular weight of approximately 73,000.
• Experimental data suggested this inhibitor is distinct from alpha1-antitrypsin.

Conclusions:

• Rat plasma contains potent kallikrein inhibitors, including a novel entity with significant inhibitory capacity.
• The characterized inhibitor exhibits broad specificity and unique biochemical properties, differentiating it from alpha1-antitrypsin.
• Further research into this novel inhibitor could reveal new therapeutic targets for conditions involving kallikrein dysregulation.