Proteins in beans

A significantly higher amoimt of protein is found in beans from South Africa compared to beans from Botswana. The amount of protein in beans from Namibia is between the contents from the two other countries (Holse et al., 2010). The variation in protein content might be due to different concentration of nitrogen in the soils. Bower et al. (1988) found that globulins are the most abimdant (53%) protein constituents in morama beans. The beans furthermore consist of albumins (23.3%), prolamins (15.5%), alkali soluble glutelins (7.7%), and acid-soluble glutelins (0.5%). 

The protein in beans is moderately low in the sulfur containing amino acids, methionine and cystine. However, the importance of this deficiency has been exaggerated, because the tests of protein quality have been conducted with rats, which have a higher requirement for these amino acids than people. The feeding of a little extra protein by serving ample portions of beans usually ensures that adequate amounts of the deficient amino acids are provided. 

Protein is an important component of most foods. Nearly everything we eat contains at least a small amount of protein. Lean meats and vegetables such as peas and beans are particularly rich in protein. In our digestive system, proteins are broken down into small molecules called a-amino acids. These molecules can then be reassembled in cells to form other proteins required by the body. 

In addition to effects on biochemical reactions, the inhibitors may influence the permeability of the various cellular membranes and through physical and chemical effects may alter the structure of other subcellular structures such as proteins, nucleic acid, and spindle fibers. Unfortunately, few definite examples can be listed. The action of colchicine and podophyllin in interfering with cell division is well known. The effect of various lactones (coumarin, parasorbic acid, and protoanemonin) on mitotic activity was discussed above. Disturbances to cytoplasmic and vacuolar structure, and the morphology of mitochondria imposed by protoanemonin, were also mentioned. Interference with protein configuration and loss of biological activity was attributed to incorporation of azetidine-2-carboxylic acid into mung bean protein in place of proline. 

Fig. 4. Backscattered Raman and ROA spectra of the n-helical protein human serum albumin in H20 (top pair) and the /3-sheet protein jack bean concanavalin A in acetate buffer solution at pH 5.4, together with MOLSCRIPT diagrams (Kraulis, 1991) of their X-ray crystal structures (PDB codes lao6 and 2cna). 

Limongelli G, Laghetti G, Perrino P, Piergiovanni AR (1996) Variation of seed storage protein in landraces of common bean (Phaseolus vulgaris L.) from Basilicata, Southern Italy. Plant Breed 119 513-516... 

Because composition and nutritional properties of the major food legumes and oilseeds have been reported in numerous technical journals and books (listed above), the section devoted to composition and chemistry highlights lesser-known but potentially important sources of plant protein that have not received the same attention. Some of these food crops have been cultivated for many years so that they are not "new" sources. Such crops as winged bean, sweet potato, tropical seeds, fruits and leaves, yams and cucurbits are potential sources of protein in areas where they are grown. These are discussed in greater detail in the remaining five chapters. 

Heat-denatured Gl exhibited a surface hydrophobicity greater than that of native Gl. The increase was not unexpected since hydrophobic groups are commonly oriented towards the center of proteins in aqueous solvents. Heat denaturation of protein exposes hydrophobic groups to the solvent. Binding of denatured Gl to bean procyanidin oligomer was predominantly hydrophobic. 

Another point to be considered is the form in which the protein-containing food is consumed and the efficiency of extraction or use of the protein in human diet. When this is considered, most of the seed-type foods, beans and legumes, have efficiencies which overcome their lowered production potential. Thus, these foods can be directly consumed and this results in a very efficient use in the human body. Many grasses and... 

Most of the applications of HPLC for protein analysis deal with the storage proteins in cereals (wheat, corn, rice, oat, barley) and beans (pea, soybeans). HPLC has proved useful for cultivar identihcation, protein separation, and characterization to detect adulterations (illegal addition of common wheat flour to durum wheat flour) [107]. Recently Losso et al. [146] have reported a rapid method for rice prolamin separation by perfusion chromatography on a RP POROS RH/2 column (UV detection at 230nm), sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE), and molecular size determination by MALDl-MS. DuPont et al. [147] used a combination of RP-HPLC and SDS-PAGE to determine the composition of wheat flour proteins previously fractionated by sequential extraction. 

The other way to study the "conductivity of protein molecules towards electron tunneling is to investigate the quenching of luminescence of electron-excited simple molecules by redox sites of proteins [95,96]. Experiments of this sort on reduced blue copper proteins have involved electron-excited Ru(II)(bpy)3, Cr(III)(phen)3, and Co(III)(phen)3 as oxidants. The kinetics of these reactions exhibit saturation at protein concentrations of 10 3 M, suggesting that, at high protein concentrations, the excited reagent is bound to reduced protein in an electron transfer precursor complex. Extensive data have been obtained for the reaction of reduced bean plastocyanin Pl(Cu(I)) with Cr(III)(phen)3. To analyze quenching experimental data, a mechanistic model that includes both 1 1 and 2 1 [Pl(Cu(I))/ Cr(III)(phen)3] complexes was considered [96]... 

In addition to their role in primary stabilization related to viscosity increase, some hydrocolloids (particularly carrageenan) are traditionally used as secondary stabilizers. Many of the primary stabilizing hydrocolloids, including locust bean gum and carboxy methyl cellulose induce precipitation of the milk proteins in the mix. This phenomenon in ice cream mix is known as wheying-off, and may be due to direct protein-polysaccharide binding and/or protein-polysaccharide incompatibility in the water phase40. The latter phenomenon may be due to decreased solvent quality due to the competition between protein and polysaccharide for solubilisation. 

Kuyvenhoven, M.W., Roszkowski, W.F., West, C.E., Hoogenboom, R.L., Vos, R.M., Beynen, A.C., and van der Meer, R. 1989. Digestibility of casein, formaldehyde-treated casein and soya-bean protein in relation to their effects on serum cholesterol in rabbits. Br. J. Nutr. 62, 331-342. 

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). 

A. sedillense aqueous extract only inhibited the radicle growth of bean 25% but tomato radicle growth 60%. In bean root, A. sedillense aqueous extract increased the expression of 16 proteins (Table 14.1, Figs. 14.1A and 14.1B). In treated-tomato roots, 14 proteins were modified. Twelve proteins increased (1-8, 10-11, 13-14), one was detected only in this treatment (9), and another one was repressed (12) (Table 14.1 and Figs. 14.1C and 14.1D). 

Maximum absorbance and relative molecular weights (M.W., kDa) of proteins modified in bean and tomato by aqueous extract of Acacia sedillense. The number of each protein corresponds to that on the 2D-gels... 

Aqueous extract of L. camara inhibited 41% and 81% bean and tomato radicle growth, respectively. However, this treatment modified a similar number of proteins in both plants. In treated-bean roots, the expression of 15 proteins was modified 6 proteins were increased (2, 8-12), and 8 were decreased (3-7 13-15) (Table 14.2, Figs. 14.2A and 14.2B). In tomato treated-roots, 11 proteins were modified six proteins were increased (1-6), and 5 were decreased (7-11) (Table 14.2, Figs. 14.2B and 14.2D). 

Aqueous extract of A. sedillense inhibited the radicle growth of bean only 25% and tomato radicle growth 60%. In spite of the difference of effects on root growth, both plants showed a similar number of modified proteins (16 and 14, respectively). In both target plants, modified proteins were increased, but this effect is more obvious in bean root. 

Mirkov, T. E, Wahlstrom, J. M., Hagiwara, K., Finardi-Filho, F., Kjemtrup, S., and Chrispeels, M. J. 1994. Evolutionary relationships among proteins in the phytohemaglutinin-arcelin-alpha-amylase inhibitor family of the common bean and its relatives. Plant Mol. Biol. 26, 1103-1113... 

Proteins that are severely deficient in one or more of the essential amino acids are called incomplete proteins. If the protein in a person s diet comes mostly from one incomplete source, the amount of human protein that can be synthesized is limited by the amounts of the deficient amino acids. Plant proteins are generally incomplete. Rice, com, and wheat are all deficient in lysine. Rice also lacks threonine, and corn also lacks tryptophan. Beans, peas, and other legumes have the most complete proteins among the common plants, but they are deficient in methionine. 

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