Trypsin Inhibitors - Manual

Two bovine pancreatic trypsin inhibitors have been isolated. Both are produced by the acinar cells and provide security against accidental trypsinogen activation and consequential unbridled proteolysis. The secretory trypsin inhibitor isolated by Kazal et al. (1948) is secreted with the zymogens into the pancreatic juice. It has been reported on by Sealock and Laskowski (1973), Schweitz et al. 1973), Greene and Giordano (1969), Cerwinsky et al. (1967) and Greene et al. (1966). It differs from the Kunitz inhibitor by forming a much less stable complex: the inhibitor is eventually digested by the trypsin. The Kazal inhibitor is active on thrombin clotting activity but does not inhibit thrombin esterase activity nor does it act upon chymotrypsin, kallikrein, plasmin, urokinase (Burch et al. 1967) or human trypsin (Feeney et al. 1969). The intracellular basic trypsin inhibitor of Kunitz was first crystallized by Kunitz and Northrop in 1936. It has been shown by Anderer and Hornle (1966) to be identical with the kallikrein inhibitor of bovine lungs and parotid gland. Chauvet and Archer (1972) report on a preparation from bovine ovary. Basic pancreatic trypsin inhibitor (BPTI) forms a very stable 1:1 complex with bovine trypsin between pH 3 and 10 (Avineri-Goldman et al. 1967; Cole and Parthasarathy 1972), and also human trypsins (Figarela et al. 1974). The dissociation constant at pH 8.0 has been reported as 6 X 10-14 Vincent and Lazdunski 1972). Chymotrypsin is also inhibited by BPTI (Blow et al. 1972) but is bound less strongly. Chauvet and Archer (1975) indicate that Lys-15 is involved in the reaction with chymotrypsin. See also Engel et al. (1974). Imhoff and Keil-Dlouhá (1971) indicate that the "chymotryptic" active site participates in the reaction with trypsin. The inhibitor-chymotrypsin complex has been crystallized (Ruhlmann et al. 1971). Plasmin is inhibited by BPTI. Summaria et al. (1975) have reported on the plasmin-inhibitor complex. Reddy and Markus (1973) have shown that BPTI forms a ternary complex with plasminogen and streptokinase that is inactive. Spilberg and Osterland (1970) indicate that it inhibits the proteolytic activity of polymorphonuclear lysosomal lysates. Sardesai and Thal (1966) report that abnormal increase in plasma proteases of pancreatitis can be reduced to normal ranges but that the normal proteolytic activity of plasma is not inhibited. The esterolytic, proteolytic and elastolytic activities of porcine elastase are not inhibited by BPTI (Gertler and Feinstein 1971). BPTI is a single polypeptide chain of 58 amino acids, including six cysteines forming three disulfide bridges (Huber et al. 1971), and having a molecular weight of 6,500. It may exist under physiological conditions as a dimer (Trautschold et al. 1967). Structure, conformation and binding studies have been reported by Creighton (1975), Geratz et al. (1975), Gelin and Karplus (1975), Quast et al. (1975), Pershina and Hvidt (1974), Vincent et al. (9174), Wang and Kassell (1974), Karplus et al. (1973), Blow et al. (1972), Wilson and Laskowski (1971). Huber et al. (1971), Liu et al. (1971), Chauvet et al. (1966), Edelhoch and Steiner (1965), Kassell and Laskowski (1965), and Gallagher et al. (1992). The inhibitor has been reviewed by Trautschold et al. (1967). Kallikreins are proteases that specifically release from kininogen an α2-globulin fraction of the serum, and biologically active polypeptides such as bradykinin and kallikin (kinin 9 and kinin 10 respectively) (Kato and Suzuki 1970; Colman et al. 1969; Trautschold et al. 1966). The kinins are very active, even in nanogram quantities, causing smooth muscle stimulation, peripheral vasodilation, enhancement of capillary permeability and pain (Lim et al. 1969), symptoms manifest in hemorrhagic or surgical shock, pancreatitis, etc. The physiologic and pathologic roles of kinins have been reviewed by Kellermayer and Graham (1968). Much information on kallikrein and hypotensive peptides may be found in the Proceedings of the International Symposium on Hypotensive Peptides (October, 1965, Florence, Italy) edited by Erdos et al. (1966). Spillerg and Osterland (1970) observed an anti-inflammatory effect of BPTI in induced acute arthritis in rabbits.

BPTI is reported to be stable in acid or neutral milieu. Its isoelectric point is 10.5 (Trautschold et al. 1967). Activity of inhibitors is usually expressed in terms of substrate inhibited. In terms of a kallikrein inhibitor one K-I unit is that quantity which inactivates 2 kallikrein units being biologically determined. Trautschold indicates there to be 6000-7000 KI units per milligram of crystalline or chromatographically purified inhibitor.