Lima bean protease

Figure 1. Thermal denaturation of selected proteinase inhibitors at pH 6.7 in 0.05 M KCl, 0.02 M CaCl . Inhibitors BPTI, bovine pancreatic trypsin inhibitor (Kunitz) PI-I and PI-II, proteinase inhibitors I and II from potato LBI, lima bean protease inhibitor 01, chicken ovoinhibitor. Heating rate, 10 C/min.

Zahniey, J. C. (1980). Independent heat stabilization of proteases associated with multi headed Inhibitors. Complexes of chymotrypsin, subtil 1 sin and trypsin with chicken ovoinhibitor and with lima bean protease Inhibitor. Blochim. Blophys. 

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). 

G proteins are located in different compartments within the cell (Nurnberg and Ahnert-Hilger, 1996). Although most G proteins are found attached to the plasma membrane and intracellular membranes, some are also located within the cytoplasm (Rudolph et al., 1989). Therefore, G proteins in preparations of disrupted cells, or in cell and tissue extracts are also subject to pertussis toxin-mediated ADP-ribosylation. In this case, precautions have to be taken to prevent proteolysis, and protease inhibitors should be included in the buffer (aprotonin, p-aminobenzamidine, leupeptin, phenylmethylsul-fonyl fluoride, or soybean or lima bean trypsin inhibitors) (Carty, 1994). 

Materials such as soybeans, lima beans, and egg whites contain natural TRY inhibitors—small polypeptides such as tti-antitrypsin (a-l-protease inhibitor) and a2-macroglob-uUn— that combine irreversibly with TRY and inactivate it by blocldng the active center. Similar nondialyzable TRY inhibitors are present in pancreatic juice, serum, and urine. These inhibitors protect plasma and other proteins against hydrolysis by TRY and other proteases if for some reason any appreciable quantity of the enzyme enters the vascular system. The absence of ai-antitrypsin is associated with an increased tendency toward panlobular emphysema in early hfe this example illustrates the effects of uninhibited proteases on organ function. 

In Hoffman (1999), the following statanent is made Some of the sources noted for various protease inhibitors and proteinase inhibitors include black-eyed peas, lima beans, kidney beans, wheat and rye germ, potatoes, bovine cartilage, bee venom, and viper venom. Human bronchial secretions and guinea pig blood are other sources. 

Snail epidermis contains at least six trypsin-kallikrein inhibitors with molecular weights ranging from 6431 to 6591 (70-72). The soybean contains two basic types of protease inhibitors, the Kunitz inhibitor of 21,500 daltons (73) and the Bowman-Birk inhibitor of 7975 daltons (74). The two are quite different proteins as shown in Figure 6. The Great Northern bean (Phaseolus vulgaris) has at least three trypsin isoinhibitors ranging in molecular weight from 8086 to 8884 (15). There are four and possibly six isoinhibitors of trypsin in lima bean (Phaseolus lunatus)(75). 

Despite the great numbers of protease and amylase inhibitors found in biological materials, more recent data indicate there is some homology among the inhibitors Comparison of the complete amino acid sequences of lima bean trypsin inhibitors I and IV shows that the two isolnhibltors differ only in that inhibitor IV contains an eight amino acid N-terminal segment and an additional two Asn residues at the C-terminal end not present in inhibitor I (75) ... 

Our study IS) revealed that the cysteine derivative facilitated inactivation of lima bean lectin in the temperature range 25 to 85°C and in the pH range 4.4 to 10.0. As with the protease inhibitors described above, the beneficial action of N-acetylcysteine is postulated to involve formation of mixed disulfide bonds between the cysteine derivative, lectins, and structural proteins in the flour. 

Protease inhibitors, compounds found in foods such as soybeans and lima beans, appear to have antitumor activity. They have been suggested as a possible factor in the lowered incidence of cancers among vegetarians. But further studies are needed. 

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