Trypsin Inhbitor, Ovomucoid

Proteins|Native Proteins

Blue ice

Molecular Weights vary between 8, 000-10, 000. The complete amino acid sequence of component IV has been reported by Tan and Stevens (1971a and b)

12352202

Isoelecttric4.5 (Kunitz 1947). Specificity: Soybean inhibitor inhibits trypsin mole-for-mole and to a lesser extent chymotrypsin. (Bidlingmeyer et al. 1972). Lanchantin et al. (1969) report soybean inhibitor to form a one-to-one complex with beef or human thrombin thus blocking its specific proteolytic capacity to activate prothrombin. Nanninga and Guest (1964) report plasmin to be inhibited. STI has been reported to inhibit leukocytic proteases. (Lieberman and Gawad 1971), but not the esterolytic, proteolytic or elastolytic activities of porcine elastase (Gertler and Feinstein 1971). Ovomucoid Ovomucoids are the glycoprotein protease-inhibitors of avian egg white. There are several protease inhibitors in egg white. One acts upon ficin and papain (Fossum and Whitaker 1968)
another, ovoinhibitor (Matsushima 1958), is a significant contaminant of crude ovomucoid preparations and acts upon bovine trypsin and chymotrypsin as well as porcine elastase and fungal proteinase (Feinstein and Gertler 1972
Gertler and Feinstein 1971
Liu et al. 1971
Tomimatsu et al. 1966). Chicken ovomucoid inhibits bovine trypsin mole for mole but does not inhibit human trypsin (Travis 1971
Feeney et al. 1969). It is electrophoretically heterogenous (Beeley and McCairns 1972
Beeley 1971
Melamed 1967
Bier et al. 1953). Both Bier and Beeley reported three major and two minor components with similar trypsin inhibiting activity but differing galactose, sialic acid and N-acetylglucosamine moieties. Ovomucoid conformation studies have been done by Murthy et al. (1973), Beeley (1972) and Donovan 1967). The arginyl residue for trypsin binding has been indicated by Liu et al. (1968). It does not contain tryptophan. The molecular weight is approximately 28, 000 (Feeney et al. 1963). Davis et al. (1971) report it as 27, 300 and Waheed and Salahuddin (1975) as 28, 500 ± 3, 500 for a distinct homogeneous variant. Specificity: Feeney et al. (1967) have shown that although ovomucoid of different species show different inhibiting specificities, their physical properties differ only slightly. Thus, Rhodes et al. (1960) have shown that golden pheasant ovomucoid inhibits only chymotrypsin whereas that from turkey inhibits both trypsin and chymotrypsin simultaneously and duck ovomucoid inhibits two moles of trypsin and one of chymotrypsin simultaneously. Lima Bean Trypsin Inhibitor Lima bean trypsin inhibitor (LBI), which inhibits bovine as well as human trypsin (Feeney et al. 1969) and plasmin (Lewis and Ferguson 1953), acts upon both trypsin and chymotrypsin by forming equimolar complexes. The binding sites are distinct and independent (Krahn and Stevens 1972, 1971). The trypsin susceptible binding site is a lys-ser peptide bond (Krahn and Stevens 1972). The site of chymotrypsin action is a leu-ser bond (Krahn and Stevens 1970). As in other protease-inhibitors the "complexing" involves a reversible hydrolysis of the peptide bond (Krahn and Stevens 1973). See also Stevens and Doskoch (1973). Lima bean trypsin inhibitors may be chromatographically separated into as many as six variants (Haynes and Feeney 1967). Jones et al. (1963) characterized four. All have similar but not identical amino acid composition, contain six or seven disulfide bonds and lack methionine and tryptophan. Molecular weights vary between 8, 000-10, 000. The complete amino acid sequence of component IV has been reported by Tan and Stevens (1971a and b). Krahn and Stevens (1972) report finding variations in activity of the four variants particularly with chymotrypsin, while essentially identical with respect to their trypsin inhibitory activity.