Proteinase inhibitors from horse plasma and leucocytes: properties and biological functions.

Alpha-1-antiproteinase (alpha 1-PI) and alpha-2-macroglobulin (alpha 2-M) from horse plasma and the proteinase inhibitor from horse leucocyte cytosol were purified and some of their physicochemical parameters estimated. Effective molar ratio, inactivation rate constants kon and apparent inhibitory constants Ki were determined for the reaction of these inhibitors and several leucocyte and pancreatic serine proteinases. It appears that alpha 1-PI, similarly to human inhibitor, controls the activity of leucocyte elastases in plasma and the lung. On the other hand, the physiological role of the leucocyte cytosol inhibitor is to protect the cytoplasm against the destructive activity of leucocyte proteinases rather than to protect the surrounding tissues.