In Vitro Enzymatic Hydrolysis of Phaseolin, the Major Storage Protein of Phaseolus Vulgaris L

Pea cell wall integrity controls the starch and protein digestion properties in the INFOGEST in vitro simulation

The cell wall microstructure has been recognized to modulate the digestibility and bioaccessibility of nutrients in whole pulse foods, while the role of cell wall integrity is unclarified in the hydrolysis of intracellular nutrients during human gastrointestinal transit. Intact pea cells were isolated to prepare a series of cell wall integrity subjected to cooking and followed by the in vitro hydrolysis of starch and protein properties using the INFOGEST 2.0 in vitro simulation. Thermal properties showed that cell samples either in raw or cooked form with different wall integrity exhibited similar and higher starch gelatinization temperatures compared to the isolated starch counterpart. It was found that intact pea cells showed the limited hydrolysis extent of the maltose (16.2%) and NH2 (6.7%) compared to the damaged cells. In addition, intact cells also withheld the cell wall integrity throughout gastrointestinal digestion with minor rupture, and presented the higher protein molecular weight (70 kDa) in the SDS-PAGE profiles. Results suggested that the in vitro starch and protein digestion properties are modulated by the cell wall integrity, which may lead to lower glycemic response and open up the possibilities of designing health food products.

Phaseolin expression in tobacco chloroplast reveals an autoregulatory mechanism in heterologous protein translation

Plastid DNA engineering is a well-established research area of plant biotechnology, and plastid transgenes often give high expression levels. However, it is still almost impossible to predict the accumulation rate of heterologous protein in transplastomic plants, and there are many cases of unsuccessful transgene expression. Chloroplasts regulate their proteome at the post-transcriptional level, mainly through translation control. One of the mechanisms to modulate the translation has been described in plant chloroplasts for the chloroplast-encoded subunits of multiprotein complexes, and the autoregulation of the translation initiation of these subunits depends on the availability of their assembly partners [control by epistasy of synthesis (CES)]. In Chlamydomonas reinhardtii, autoregulation of endogenous proteins recruited in the assembly of functional complexes has also been reported. In this study, we revealed a self-regulation mechanism triggered by the accumulation of a soluble recombinant protein, phaseolin, in the stroma of chloroplast-transformed tobacco plants. Immunoblotting experiments showed that phaseolin could avoid this self-regulation mechanism when targeted to the thylakoids in transplastomic plants. To inhibit the thylakoid-targeted phaseolin translation as well, this protein was expressed in the presence of a nuclear version of the phaseolin gene with a transit peptide. Pulse-chase and polysome analysis revealed that phaseolin mRNA translation on plastid ribosomes was repressed due to the accumulation in the stroma of the same soluble polypeptide imported from the cytosol. We suggest that translation autoregulation in chloroplast is not limited to heteromeric protein subunits but also involves at least some of the foreign soluble recombinant proteins, leading to the inhibition of plastome-encoded transgene expression in chloroplast.

Growth Impairment Caused by Raw Linseed Consumption: Can Trypsin Inhibitors Be Harmful for Health?

Linseed (Linun usitatissimum L.) is an important oilseed whose nutritional value can be impaired due to presence of antinutritional factors and low protein digestibility. Protein fractions from raw linseed meal were extracted, isolated and analyzed in vitro and in vivo. Globulins, the major protein fraction of linseed, showed low in vitro susceptibility to trypsin and chymotrypsin, but its in vivo digestibility was 93.2 %. Albumin fraction had high trypsin inhibition activity (5250 Inhibition Units g(-1)) and presented low molecular mass protein bands, similar to known trypsin inhibitors. Raw linseed consumption caused negative effects on rat growth and reduction of intestinal villi. Results indicate that raw linseed meal must not be used as an exclusive source of protein regardless of the major proteins have high digestibility; digestive enzymes inhibitors in raw linseed probably reduces the protein utilization.

Enrichment of ACE inhibitory peptides in navy bean (Phaseolus vulgaris) using lactic acid bacteria

The present study was conducted to explore a novel strategy to enhance angiotensin I-converting enzyme (ACE) inhibitory activities of navy bean by preparation of navy bean milk (NBM) which was then subjected to fermentation of four lactic acid bacteria (LAB) strains.

Nutritional and health perspectives of beans (Phaseolus vulgaris L.): an overview

Beans, the variants of Phaseolus vulagris, are nutritionally and economically important food crop in each part of the world. Besides providing nutrients such as multifaceted carbohydrates, elevated proteins, dietary fiber, minerals, and vitamins, these also contain rich variety of polyphenolic compounds with prospective health benefits. This review mainly focuses the important nutritional aspects of beans as well as their contribution in decreasing the risks of chronically degenerative diseases.

A plant secretory signal peptide targets plastome-encoded recombinant proteins to the thylakoid membrane

Plastids are considered promising bioreactors for the production of recombinant proteins, but the knowledge of the mechanisms regulating foreign protein folding, targeting, and accumulation in these organelles is still incomplete. Here we demonstrate that a plant secretory signal peptide is able to target a plastome-encoded recombinant protein to the thylakoid membrane. The fusion protein zeolin with its native signal peptide expressed by tobacco (Nicotiana tabacum) transplastomic plants was directed into the chloroplast thylakoid membranes, whereas the zeolin mutant devoid of the signal peptide, Δzeolin, is instead accumulated in the stroma. We also show that zeolin folds in the thylakoid membrane where it accumulates as trimers able to form disulphide bonds. Disulphide bonds contribute to protein accumulation since zeolin shows a higher accumulation level with respect to stromal Δzeolin, whose folding is hampered as the protein accumulates at low amounts in a monomeric form and it is not oxidized. Thus, post-transcriptional processes seem to regulate the stability and accumulation of plastid-synthesized zeolin. The most plausible zeolin targeting mechanism to thylakoid is discussed herein.

Phaseolin from Phaseolus vulgaris bean modulates gut mucin flow and gene expression in rats

Dietary protein might modulate mucin flow and intestinal mucin gene expression. Since unheated phaseolin from Phaseolus vulgaris bean is resistant to digestion and increases gut endogenous protein losses, we hypothesised that unheated phaseolin influences mucin flow and gene expression, and that phaseolin heat treatment reverses these effects. The hypothesis was tested using a control diet containing casein as the sole protein source and three other diets with casein being replaced by 33 and 67 % of unheated and 67 % of heated phaseolin. The rats were fed for 6 d and euthanised. Digesta and faeces were collected for determining digestibility and mucin flow. Gut tissues were collected for mucin (Muc1, Muc2, Muc3 and Muc4) and Trefoil factor 3 (Tff3) gene expressions. Colonic mucin flow decreased linearly with increasing the dietary level of unheated phaseolin (P < 0·05). Unheated phaseolin increased N flow in ileum, colon and faeces (P < 0·05), and reduced apparent N digestibility linearly (P < 0·01). Heat treatment reversed all these changes (P < 0·05 to < 0·001), except mucin flow. The expressions of Muc mRNA in gut tissues were influenced by dietary phaseolin level (ileum and colon: Muc3 and Muc4) and thermal treatment (ileum: Muc2; colon: Muc2, Muc3, Muc4 and Tff3) (P < 0·05 to 0·001). In conclusion, phaseolin modulates mucin flow and Muc gene expression along the intestines differentially.

An engineered C-terminal disulfide bond can partially replace the phaseolin vacuolar sorting signal

Seed storage proteins accumulate either in the endoplasmic reticulum (ER) or in vacuoles, and it would appear that polymerization events play a fundamental role in regulating the choice between the two destinies of these proteins. We previously showed that a fusion between the Phaseolus vulgaris vacuolar storage protein phaseolin and the N-terminal half of the Zea mays prolamin gamma-zein forms interchain disulfide bonds that facilitate the formation of ER-located protein bodies. Wild-type phaseolin does not contain cysteine residues, and assembles into soluble trimers that transiently polymerize before sorting to the vacuole. These transient interactions are abolished when the C-terminal vacuolar sorting signal AFVY is deleted, indicating that they play a role in vacuolar sorting. We reasoned that if the phaseolin interactions directly involve the C terminus of the polypeptide, a cysteine residue introduced into this region could stabilize these transient interactions. Biochemical studies of two mutated phaseolin proteins in which a single cysteine residue was inserted at the C terminus, in the presence (PHSL*) or absence (Delta 418*) of the vacuolar signal AFVY, revealed that these mutated proteins form disulphide bonds. PHSL* had reduced protein solubility and a vacuolar trafficking delay with respect to wild-type protein. Moreover, Delta 418* was in part redirected to the vacuole. Our experiments strongly support the idea that vacuolar delivery of phaseolin is promoted very early in the sorting process, when polypeptides are still contained within the ER, by homotypic interactions.

Enzymatic hydrolysis of sweet lupin, chickpea, and lentil 11S globulins decreases their antigenic activity

We investigated the effects of treatments with the enzymes pepsin and trypsin on the in vitro immunological reactivity of the major globulins found in the seeds of sweet lupin, chickpea, and lentil. Polyclonal major globulin-specific antiserum was obtained by immunization of rabbits with a solution of the 11S globulin of each legume. The globulins were hydrolyzed with pepsin and trypsin for 1, 5, 15, and 30 min. The native globulins and their hydrolysates were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting to identify the polypeptide bands with antigenic activity, and the hypoantigenicity of the hydrolysates was analyzed by enzyme-linked immunosorbent assay. Our results show that enzymatic treatment of the major storage protein (11S globulin) of sweet lupin, chickpea, and lentil with pepsin or trypsin lead to the formation of large amounts of short peptides and free amino acids that do not allow antibody binding, resulting in a weakened immunoreactivity.

Susceptibility of phaseolin to in vitro proteolysis is highly variable across common bean varieties (Phaseolus vulgaris)

A study was conducted to investigate the amino acid (AA) composition and the susceptibility to in vitro proteolysis (pepsin, 120 min and pancreatin, 240 min) of a collection of purified phaseolins ( n = 43) in unheated or heat-treated form. The AA composition of phaseolin varied little across bean varieties. At 360 min of in vitro proteolysis, the degree of hydrolysis varied from 11 to 27% for unheated and from 57 to 96% for heated phaseolins ( P < 0.001). Heat treatment markedly increased the susceptibility of phaseolin to proteolysis ( P < 0.001). The AA scores (AAS) and the protein digestibility corrected for AAS indicated S-containing AA as the limiting AA (39 +/- 3 and 30 +/- 5%, respectively). In conclusion, susceptibility to proteolysis of heat-treated phaseolin rather than its AA composition affects the nutritional value of phaseolin estimated in vitro. Therefore, it should be the criterion of choice in breeding programs aimed at improving the nutritional value of common beans for humans.

Phaseolin type and heat treatment influence the biochemistry of protein digestion in the rat intestine

The study aimed to investigate thein vivodigestion ofPhaseolus vulgarisphaseolin types differing in their subunit pattern composition. Diets contained either casein as the sole source of protein or a mixture (1:1) of casein and pure Sanilac (S), Tendergreen (T) or Inca (I) phaseolin either unheated or heated. Rats were fed for 11 d with the experimental diets. Their ileal content and mucosa were collected and prepared for electrophoresis, Western blotting, densitometry and MS. Differences in digestion among native phaseolin types were observed for intact phaseolin at molecular weights (MW) of 47–50·5 kDa and for an undigested fragment at MW of 19–21·5 kDa in ileal digesta. In both cases, the concentration of these protein bands was lower for I phaseolin than for S or T phaseolin (P < 0·05). In the mucosa, the concentration of a protein band at MW of 20·5–21·5 kDa was lower for S phaseolin as compared to T or I phaseolin (P < 0·001). The presence of phaseolin subunits and their fragments was confirmed by Western blotting. MS analysis revealed the presence of undigested α and β subunit fragments from phaseolin and endogenous proteins (anionic trypsin I and pancreatic α-amylase) in ileal digesta. Thermal treatment improved digestion (P < 0·01), acting on both dietary and endogenous protein components. In conclusion, this study provides evidence for differences in intestinal digestion among phaseolin types, S phaseolin being more resistant and I phaseolin more susceptible. These differences were affected by the origin of the phaseolin subunit precursor. Heat treatment enhanced phaseolin digestion.

Influence of thePhaseolus vulgarisphaseolin level of incorporation, type and thermal treatment on gut characteristics in rats

Phaseolus vulgarisphaseolin has been shown to stimulate faecal losses of endogenous N in rats. Experiments with purified phaseolin were carried out in rats to test the hypothesis that these losses reflect intestinal disorders. Phaseolin composition varies depending on its constitutive subunits. Therefore, three phaseolin types (S, T, I) were tested. Phaseolin T was incorporated in varying levels (0, 33, 67 or 100% of the dietary protein) as raw material in experiment 1. In experiment 2, the three phaseolin types were incorporated at 50%, with or without previous thermic treatment. Raw casein was the basal protein source and was also heated in experiment 2. Faecal digestibility of phaseolin and gut integrity were evaluated in both experiments. The incorporation level or type of phaseolin had little effect on gross anatomy of gut segments but these factors influenced the weight and pH of fresh contents of the stomach and caecum (P<0·05). Raw phaseolin T incorporated at various levels led to an enlargement of duodenal villi together with a tendency for increased crypt depth in the jejunum (P=0·06). Activities of both alkaline phosphatase in the duodenum and aminopeptidase N in the ileum decreased (P<0·05) after thermal treatment of casein while they increased (P<0·05) for heat-treated phaseolin S and T, respectively. In conclusion, raw phaseolin had no effect on the tissue weight of gut segments and induced limited alterations in the small intestine. Differences due to phaseolin level or type were limited too.

Grain legume proteins and nutraceutical properties

Grain legumes are a valuable source of food proteins. Their exploitation is expected to grow in relation of a growing world's food needs. Moreover, it is currently taking place a reappraisal of the beneficial effects of legume seed dietary intake, which are the basis for various health claims. Proteins and peptides concur to the observed biological activities of legume seeds, but their effect(s) has(ve) not completely been disclosed. Aims of this review are: to report the most relevant putative positive effects of grain legumes on human health and to give an account of the current knowledge on the demonstrated legume seed protein biological activities. Specific effects on the prevention and treatment of various diseases, mostly of which are typical of the affluent countries, are reported. Examples of studies at molecular level aimed at elucidating of the underlying mechanism(s) are given. The prospects on targeted legume protein exploitation in the nutraceutical area, including the biotechnological approaches, are also considered.

The major peanut allergen, Ara h 2, functions as a trypsin inhibitor, and roasting enhances this function

BACKGROUND

The widespread use of peanut products, the severity of the symptoms, and its persistence in afflicted individuals has made peanut allergy a major health concern in western countries such as the United States, United Kingdom, and Canada. In a previous study, the authors showed that the allergenic properties of peanut proteins are enhanced as a result of thermal processing.

OBJECTIVE

The purpose of this investigation was to determine whether any specific functions are associated with the major peanut allergen, Ara h 2, and whether the functionality of this protein is influenced by processing. An assay was developed and used to assess structure/function changes in Ara h 2 induced by roasting and the effect of these alterations on the allergenic properties of this major peanut allergen.

METHODS

A protein domain homology search was used to determine possible functions for Ara h 2. One of the putative functions (protease inhibition) was tested by means of appropriate enzyme assays and protein gel electrophoresis. Circular dichroism was used to compare the structural properties of Ara h 2 purified from raw and roasted peanuts.

RESULTS

Ara h 2 purified from peanuts is homologous to and functions as a trypsin inhibitor. Roasting caused a 3.6-fold increase in trypsin inhibitory activity. Functional and structural comparison of the Ara h 2 purified from roasted peanuts to native and reduced Ara h 2 from raw peanuts revealed that the roasted Ara h 2 mimics the behavior of native Ara h 2 in a partially reduced form.

CONCLUSIONS

The data indicate that thermal processing might play an important role in enhancing the allergenic properties of peanuts. Not only has it previously been shown to affect the structural and allergic properties of peanut proteins but also, for the first time, the functional characteristics of an allergen. These structural and functional alterations are likely to influence the allergenicity of peanuts.

Dry bean protein functionality

Dry beans are an important source of proteins, carbohydrates, dietary fiber, and certain minerals and vitamins in the human food supply. Among dry beans, Phaseolus beans are cultivated and consumed in the greatest quantity on a worldwide basis. Typically, most dry beans contain 15 to 25% protein on a dry weight basis (dwb). Water-soluble albumins and salt-soluble globulins, respectively, account for up to 10 to 30% and 45 to 70% of the total proteins (dwb). Dry bean albumins are typically composed of several different proteins, including lectins and enzyme inhibitors. A single 7S globulin dominates dry bean salt soluble fraction (globulins) and may account for up to 50 to 55% of the total proteins in the dry beans (dwb). Most dry bean proteins are deficient in sulfur amino acids, methionine, and cysteine, and therefore are of lower nutritional quality when compared with the animal proteins. Despite this limitation, dry beans make a significant contribution to the human dietary protein intake. In bean-based foods, dry bean proteins also serve additional functions that may include surface activity, hydration, and hydration-related properties, structure, and certain organoleptic properties. This article is intended to provide an overview of dry bean protein functionality with emphases on nutritional quality and hydration-related properties.

Protease C2, a cysteine endopeptidase involved in the continuing mobilization of soybean beta-conglycinin seed proteins

The protease that degrades the beta subunit of the soybean (Glycine max (L.) Merrill) storage protein beta-conglycinin was purified from the cotyledons of seedlings grown for 12 days. The enzyme was named protease C2 because it is the second enzyme to cleave the beta-conglycinin storage protein, the first (protease C1) being one that degrades only the alpha' and alpha subunits of the storage protein to products similar in size and sequence to the remaining intact beta subunit. Protease C2 activity is not evident in vivo until 4 days after imbibition of the seed. The 31 kDa enzyme is a cysteine protease with a pH optimum with beta-conglycinin as substrate of 5.5. The action of protease C2 on native beta-conglycinin produces a set of large fragments (52-46 kDa in size) and small fragments (29-25 kDa). This is consistent with cleavage of all beta-conglycinin subunits at the region linking their N- and C-domains. Protease C2 also cleaves phaseolin, the Phaseolus vulgaris vicilin homologous to beta-conglycinin, to fragments in the 25-28 kDa range. N-Terminal sequences of isolated beta-conglycinin and phaseolin products show that protease C2 cleaves at a bond within a very mobile surface loop connecting the two compact structural domains of each subunit. The protease C2 cleavage specificity appears to be dictated by the substrate's three-dimensional structure rather than a specificity for a particular amino acid or sequence.

The effects of roasting on the allergenic properties of peanut proteins

BACKGROUND

Because of the widespread use of peanut products, peanut allergenicity is a major health concern in the United States. The effect or effects of thermal processing (roasting) on the allergenic properties of peanut proteins have rarely been addressed.

OBJECTIVE

We sought to assess the biochemical effects of roasting on the allergenic properties of peanut proteins.

METHODS

Competitive inhibition ELISA was used to compare the IgE-binding properties of roasted and raw peanut extracts. A well-characterized in vitro model was used to test whether the Maillard reaction contributes to the allergenic properties of peanut proteins. The allergic properties were measured by using ELISA, digestion by gastric secretions, and stability of the proteins to heat and degradation.

RESULTS

Here we report that roasted peanuts from two different sources bound IgE from patients with peanut allergy at approximately 90-fold higher levels than the raw peanuts from the same peanut cultivars. The purified major allergens Ara h 1 and Ara h 2 were subjected to the Maillard reaction in vitro and compared with corresponding unreacted samples for allergenic properties. Ara h 1 and Ara h 2 bound higher levels of IgE and were more resistant to heat and digestion by gastrointestinal enzymes once they had undergone the Maillard reaction.

CONCLUSIONS

The data presented here indicate that thermal processing may play an important role in enhancing the allergenic properties of peanuts and that the protein modifications made by the Maillard reaction contribute to this effect.

Structure of the major peanut allergen Ara h 1 may protect IgE-binding epitopes from degradation

In the past decade, there has been an increase in allergic reactions to peanut proteins, sometimes resulting in fatal anaphylaxis. The development of improved methods for diagnosis and treatment of peanut allergies requires a better understanding of the structure of the allergens. Ara h 1, a major peanut allergen belonging to the vicilin family of seed storage proteins, is recognized by serum IgE from >90% of peanut-allergic patients. In this communication, Ara h 1 was shown to form a highly stable homotrimer. Hydrophobic interactions were determined to be the main molecular force holding monomers together. A molecular model of the Ara h 1 trimer was constructed to view the stabilizing hydrophobic residues in the three dimensional structure. Hydrophobic amino acids that contribute to trimer formation are at the distal ends of the three dimensional structure where monomer-monomer contacts occur. Coincidentally, the majority of the IgE-binding epitopes are also located in this region, suggesting that they may be protected from digestion by the monomer-monomer contacts. On incubation of Ara h 1 with digestive enzymes, various protease-resistant fragments containing IgE-binding sites were identified. The highly stable nature of the Ara h 1 trimer, the presence of digestion resistant fragments, and the strategic location of the IgE-binding epitopes indicate that the quaternary structure of a protein may play a significant role in overall allergenicity.

Stability of food allergens to digestion in vitro

An integral part of the safety assessment of genetically modified plants is consideration of possible human health effects, especially food allergy. Prospective testing for allergenicity of proteins obtained from sources with no prior history of causing allergy has been difficult because of the absence of valid methods and models. Food allergens may share physicochemical properties that distinguish them from nonallergens, properties that may be used as a tool to predict the inherent allergenicity of proteins newly introduced into the food supply by genetic engineering. One candidate property is stability to digestion. We have systematically evaluated the stability of food allergens that are active via the gastrointestinal tract in a simple model of gastric digestion, emphasizing the major allergens of plant-derived foods such as legumes (peanuts and soybean). Important food allergens were stable to digestion in the gastric model (simulated gastric fluid). For example, soybean beta-conglycinin was stable for 60 min. In contrast, nonallergenic food proteins, such as spinach ribulose bis-phosphate carboxylase/oxygenase, were digested in simulated gastric fluid within 15 sec. The data are consistent with the hypothesis that food allergens must exhibit sufficient gastric stability to reach the intestinal mucosa where absorption and sensitization (development of atopy) can occur. Thus, the stability to digestion is a significant and valid parameter that distinguishes food allergens from nonallergens.

Hard-to-cook phenomenon in common beans--a review

Legumes are one of the world's most important sources of food supply, especially in developing countries, in terms of food energy as well as nutrients. Common beans are a good source of proteins, vitamins (thiamine, riboflavin, niacin, vitamin B6) and certain minerals (Ca, Fe, Cu, Zn, P, K, and Mg). They are an excellent source of complex carbohydrates and polyunsaturated free fatty acids (linoleic, linolenic). However, common beans have several undesirable attributes, such as long cooking times, being enzyme inhibitors, phytates, flatus factors, and phenolic compounds, having a "beany" flavor, and being lectins and allergens, which should be removed or eliminated for effective utilization. Grain quality of common beans is determined by factors such as acceptability by the consumer, soaking characteristics, cooking quality, and nutritive value. Acceptability characteristics include a wide variety of attributes, such as grain size, shape, color, appearance, stability under storage conditions, cooking properties, quality of the product obtained, and flavor. Storage of common beans under adverse conditions of high temperature and high humidity renders them susceptible to a hardening phenomenon, also known as the hard-to-cook (HTC) defect. Beans with this defect are characterized by extended cooking times for cotyledon softening, are less acceptable to the consumer, and are of lower nutritive value. Mechanisms involved in the HTC defect have not been elucidated satisfactorily. Attempts to provide a definitive explanation of this phenomenon have not been successful. The most important hypotheses that have been proposed to explain the cause of bean hardening are (1) lipid oxidation and/or polymerization, (2) formation of insoluble pectates, (3) lignification of middle lamella, and (4) multiple mechanisms. Most researchers have reported that the defect develops in the cotyledons. Recently, some authors have suggested that the seed coat plays a significant role in the process of common bean hardening. A better knowledge of cotyledon and seed coat microstructure may lead to a better understanding of the causes of seed hardness. In order to prevent the development of the HTC defect several procedures have been proposed: (1) appropriate storage, (2) controlled atmospheres, and (3) pretreatments. Probably, the most workable solution to the hardening phenomenon may be the development of materials less prone to HTC phenomenon. Decreasing cooking time, increasing nutritive value, and improving sensory properties of seeds with HTC defect would have great nutritional and economical impact.(ABSTRACT TRUNCATED AT 400 WORDS)

Conformational characteristics of legume 7S globulins as revealed by circular dichroic, derivative u.v. absorption and fluorescence techniques

The 7S globulin storage proteins, phaseolin, vicilin, and beta-conglycinin of, respectively, dry bean, field pea, and soybean, are highly homologous, have similar predicted protein structures, and yet exhibit considerable differences in their susceptibility to various proteinases [Nielsen, S.S., Deshpande, S.S., Hermodson, M.A. & Scott, M.P. (1988) J. Agric. Food Chem. 36, 896-902]. These differences in their proteolytic behavior were studied in relation to their solution conformational states. The secondary structures of these three proteins determined by far u.v. circular dichroism were characterized by predominantly beta-sheet and beta-turn parameters. However, characterization of tertiary and quaternary structures using second derivative u.v. absorption spectroscopy, surface hydrophobicity using cis-parinaric acid as hydrophobic probe, and fluorescence quenching studies of intrinsic Trp fluorescence using an ionic (iodide) and a neutral (acrylamide) quencher indicated sharp differences in the conformation of these proteins. About 9.6 and 10.2 out of 13 and 15 tyrosyls/subunit of phaseolin and beta-conglycinin, respectively, were exposed to polar solvent, while the surface hydrophobicity varied beta-conglycinin greater than vicilin greater than phaseolin. The Trp residues in phaseolin were not accessible to iodide, while half those of vicilin and beta-conglycinin were quenched. The order of Trp accessibility to acrylamide was vicilin greater than beta-conglycinin greater than phaseolin. The relative compactness of these three proteins based on these studies was related to the observed differences in their susceptibility to various proteinases.