Lima bean inhibitors

Plant - Inhibitors derived from plant sources include the black bean or soybean inhibitors (Kunltz and Bowman-Birk types),34-57 lima bean inhibitor, 38 and chickpea inhibitor.39 These are all unusual double-headed polypeptides, with two Independent reactive sites, capable of interacting with both trypsin and chymotrypsin.60-63 They also are inhibitors of granulocyte elastase and cathepsin... 

Figure 2. Effect of pH and N-acetylcysteine (NAC) on trypsin inhibitory activity of lima bean inhibitor at 45 C. Upper plot, no NAC lower plot, with NAC.

Aletor, V.A. and B.L. Fetuga. 1988. The interactive effects of lima bean (Phaseolus lunatus) trypsin inhibitor, hemagglutinin and cyanide on some hepatic dehydrogenases, ornithine carbamoyltransferase and intestinal disaccharidases in weanling rats. Veterin. Human Toxicol. 30 540-544. 

An additional emission band near 350 nm has been observed for lima bean trypsin inhibitor (LBTI).(173) The authors discussed both the possibility of contamination by tryptophan and excited-state tyrosinate formation. Since this 350-nm emission has a tyrosine-like excitation spectrum that is slightly shifted compared to that of the major 302-nm emission, it is also possible that the tyrosine residue in a fraction of the LBTI molecules could be hydrogen bonded. This model is supported by the observations that the phenol side chain is shielded from solvent and has an anomalously high pKa. 

X.-Y. Liu, K. O. Cottrell, and T. M. Nordlund, Spectroscopy and fluorescence quenching of tyrosine in lima bean trypsin/chymotrypsin inhibitor and model peptides, Photochem. 

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). 

Enzyme Bovi ne pancreati c trypsin inhibitor Lima bean trypsin inhibitor Soybean trypsin inhibitor Ovomucoi d... 

Lima-bean lectin precipitated blood-group A and B secretor saliva, but not O it did not precipitate the saliva of any nonsecretors.2,3,103 Kriipe77 substantiated Boyd s results, using secretor saliva as an inhibitor of lima-bean lectin-erythrocyte agglutination. Types A,B, A,A2, AiO, and A20 saliva all inhibited the lima-bean lectin, whereas type OO saliva and type OO ovarian-cyst material were noninhibitory. 

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. 

The major plasma inhibitor of Factor XIa is Uj-antitrypsin while antithrombin III, in the presence or absence of heparin, plays a minor role in controlling this enzyme (S5). Interestingly, plant inhibitors like soybean, com, and lima bean trypsin inhibitors are able to block Factor Xlla and kallikrein but only mildly inhibit Factor XI. Thus, one can use these agents to minimize cross-reactivity in an indirect s)mthetic substrate assay for Factor XIa. 

The carbohydrate-binding specificity of the lima bean lectin studied by inhibition of precipitation, and a sulfhydryl group protection assay [161], revealed the type A trisaccharide GalNAc(al-3)[L-Fuc(al-2)]Gal to be the best inhibitor, 40 times more potent than GalNAc. The a-glycosides of GalNAc are 8 times more potent than the corresponding 3-anomers. 

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) ... 

There is great homology between the Bowman-Birk soybean trypsin inhibitor (89), lima bean trypsin inhibitor IV (75) and the Great Northern trypsin inhibitor II (90) as shown in Table VIII The tryptic peptide maps of Great Northern isoinhibitors I and mb were very similar while isoinhibitors I and II had no peptides in common (15) ... 

Table VIII. Amino Acid Sequence Homology Among the Bowman-Birk Soybean Trypsin Inhibitor (BB 89)> Lima Bean Trypsin Inhibitor IV (LB 75) and Great Northern Bean Trypsin Inhibitor II (GB 90)...

XII Hageman factor The first factor in the intrinsic pathway. A/, 74000 (bovine), 76000 (human). Single chain glycoprotein. Activated by plasmin, kallikrein and XII,. Inhibited by antithrombin III (inhibition accelerated by heparin). Cl esterase inhibitor and lima bean trypsin inhibitor. Activation of XII initiated by contact with abnormal surfaces. 

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. 

---