Trypsin inhibitors legumes

Some legumes, including raw soy or peanut flour are known to contain certain antinutritional factors such as proteinase inhibitors and hemagglutinins or lectins (21,22). These factors can be inactivated, for the most part, by moist heat, during processing. Interestingly, peanut flour contained more trypsin inhibitor and lectin than did soy flour (22). 

It was noted, however, that legume seeds contain anti nutritional factors such as trypsin inhibitors and lectins which exert... 

Faba beans contain several ANFs such as tannins, protease inhibitors (vicin/ convicin) and lectins. Use of low-vicin/convicin cultivars may allow substantial levels of faba beans to be included in poultry diets (Danner, 2003). The levels of trypsin inhibitor and lectin activities are low compared with other legume seeds and do not pose problems in poultry diets when faba beans are incorporated into diets at the levels shown below. Of most concern for poultry is the tannin fraction, which has been shown to depress digestibility of the protein and AA (Ortiz et al., 1993). Tannins in whole faba beans are associated with the seedcoat (testa), and the tannin content is related to the colour of the seedcoat (and flowers). Tannins are lower in white than in the colour-seeded varieties. 

The Bowman-Birk type protease inhibitors represent a class of low molecular weight, cysteine-rich proteins found in legume seeds (.10). The major Bowman-Birk inhibitor in soybean seeds is a double-headed protein capable of blocking the activity of both trypsin and chymotrypsin. This protein represents approximately 4% of the total protein in soybean seeds (1J ). In contrast to the soybean trypsin inhibitor (Kunitz), the "double-headed inhibitor (referred to as BB) is typical of protease inhibitors present in a large number of legume seeds for example, peanuts (12) chick peas (33)5 kidney beans (3JO adzuki beans (33) lima beans (16). 

Burks, A.W., Cockrell, G., Connaughton, C. et al. 1994. Identification of peanut agglutinin and soybean trypsin inhibitor as minor legume allergens. Int Arch Allergy Immunol 105 143-149. 

Some of the proteins are toxic in nature. Ricin present in castor bean is extremely toxic to higher animals in very small amounts. Enzyme irvhibitors such as trypsin inhibitor bind to digestive enzyme and prevent the availability of the protein. Lectin, a toxic protein present commonly in legumes, agglutinates red blood cells. A bacterial toxin causes cholera, which is a protein. Snake venom is protein in nature. 

Legume seeds contain a number of antinutritive components, mainly lectin and trypsin inhibitors. The efficiency of the nutritional utilization of diets containing soybean is well below that expected on the basis of chemical composition [196]. In order to reduce the extent of this constraint, at present, all soy products go through expensive heat treatment or other processing procedures that can lead to losses of essential amino acids and to the production of toxic by-products. It is hoped that an effective strategy will help improve the nutritional value of soy proteins [197,198]. 

This potent trypsin inhibitor is structurally similar to legume Ser protease inhibitors and is stabilized by two 3 strands and a disulfide bond. 

Proteins are found in all organisms, play many roles, and vary widely in structure and properties. The enzyme ribulose 1,5-bisphosphate carboxylase (EC 4.1.1.39) is probably the world s most abundant protein, as it is the major protein present (up to 50%) in the leaves of plants (Ramshaw, 1982). However, in the following discussion, only those proteins with toxic or inhibitory properties to animals or fungi or other noteworthy activity will be discussed. Several groups of proteins from plants are known to be toxic to animals. The most important group of these is called lectins or hemagglutinins. Many legume seeds also contain protease (or trypsin) inhibitors (Weder, 1981). Similar compounds are found in plants of the Solanaceae (Ramshaw, 1982). 

A number of proteinase inhibitors, often called trypsin inhibitors, are known to occur in seeds of legumes (Ryan, 1981 Weder, 1981). These polypeptides often inhibit both trypsin and chymotrypsin and block digestion of many legume seeds. Cooking deactivates most of these compounds. 

In summary, nutritional improvement may result from inactivation of trypsin inhibitors and introduction of new disulfide bonds via sulfhydryl-disulfide interchange and oxidation reaction among added thiols, inhibitors, and structural proteins. Such an approach should be useful for inactivating related disulfide-containing toxic compounds such as lectins (hemagglutinins) and ricin, widely distributed in legumes and castor beans, respectively. 

Cooperative effects of heat and thiols in activating trypsin inhibitors from legumes in solution and in the solid state. 

Buckwheat [Pagopyrum esctdentum, Polygonaceae) contains the inhibitor BTl (Buckwheat Trypsin Inhibitor), and, correspondingly, three isoinhibitors of the Bowman-Birk type that are called BTl-1, BTl-2 and BTl-3, which consist of a single polypeptide chain containing 69 amino acids. The content of protease inhibitors in selected legumes is shown in Table 10.1. 

The composition of the major alkaloids of different lupine seed species is shown in Table 10.3. The main alkaloids of white lupine seeds are lupanine and albine, of blue lupine seeds lupanine and 13-hydroxylupanine and of yellow lupine seeds lupinine and sparteine. The content of other toxic and antinutritional substances (lectins, trypsin inhibitors and phytates) in lupine seeds is similar to the content of other legume seeds. 

Some of the best investigated anti-nutrients are the enzyme inhibitors present in legumes and other plants. The Bowman-Birk and the Kunitz inhibitors of trypsin and other proteases are among the best characterized. In contrast to the non-specific and widespread influences of tannins and lectins (Carmona, 1996), the Bowman-Birk, Kunitz and other such inhibitors target specific enzymes. Corresponding with this, proteases and other digestive enzymes vary in sensitivity to the different inhibitors. 

Enzyme inhibitors of a protein nature are of significant concern because of widespread occurrence. The most common of these affect the pancreatic enzymes, trypsin and chymotrypsin. and arc found in legumes, as well as in egg whites and potatoes. 

Inhibitor activity is normally determined with commercial animal enzymes, e. g., bovine trypsin or bovine chymotrypsin. The evaluation of a potential effect of the inhibitors on human health assumes that the inhibition of human enzymes is known. Present data show that inhibitors from legumes generally inhibit human trypsin to the same extent or a little less than bovine trypsin. On the other hand, human chymotrypsin is inhibited to a much greater extent by most legumes. Ovomucoid and ovoinhibitor from egg white as well as the Kazal inhibitor from bovine pancreas do not inhibit the human enzymes. The Kunitz inhibitor from bovine pancreas inhibits human trypsin but not chymotrypsin. The data obtained greatly depend not only on the substrate used, but also on the enzyme preparation and the reaction conditions, e. g., on the ratio enzyme/inhibitor. The stability of an inhibitor as it passes through the stomach must also be taken into account in the evaluation of a potential effect (cf. Table 16.15). The Kunitz inhibitor of soybeans, for... 

Inhibitors of the Bowman-Birk type have a relative molecular weight of about 6-10 kDa, a higher number of disulfide bridges, and exhibit specificity against trypsin and chymotrypsin, as they contain two independent binding sites in the molecule. Bowman-Birk type inhibitors belong to the most common inhibitors. They occur in legumes, cereals, pseudocereals, potatoes and some other materials. 

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