Molecular size, subunit structure and microheterogeneity of glycoprotein II from the seeds of kidney bean (Phaseolus vulgaris L.)

The isolation of Glycoprotein II from the seeds of kidney bean (Phaseolus vulgaris) cv. 'Processor' is described. This glycoprotein was shown by SDS-gel electrophoresis to dissociate into four subunits, 53 000, 50 000, 47 000 and 43 000 (alpha : beta : gamma : delta), in an approximate ratio of 2 : 0.2 : 2 : 1. At neutral and slightly alkaline pH values its molecular weight was about 142 000 (protomer) while at pH 5 it was mainly in the form of a tetramer with a molecular weight value of about 560 000. Samples of Glycoprotein II were shown by isoelectric focusing, molecular sieve chromatography and immunochemical methods to be microheterogenous. A number of fractions were prepared by these methods in which the proportion of the major subunits (alpha : gamma : delta) varied between 1 : 1 : 1 to 3 : 3 : 1. These ratios were also shown to change during development of the seed. On the basis of these results it is suggested that, at and above pH 7, samples of Glycoprotein II consist of microheterogenous population of molecules each containing three subunits per protomer. However, in these protomers the subunits are drawn, in different ratios, from the four subunits available. When the net molecular charge is small, at and around the isoelectric zone of Glycoptotein II, the protomer is converted mainly into the more stable tetramer containing 12 subunits.

Immunocytochemical localization of ingested kidney bean (Phaseolus vulgaris) lectins in rat gut

The binding of ingested kidney bean (Phaseolus vulgaris) lectins to the luminal surface of the rat gut was investigated by an indirect immunofluorescence method in which the primary antiserum was monospecific for kidney bean globulin lectins. The major lectin-positive sites were found to be the non-crypt regions of villi in the proximal region of the small intestine; exactly the same regions displayed extensive disruption of microvilli. Lectins were not localized in the brush border regions of ileal villi and no microvillus abnormalities were detected in this region of the gut. The luminal surface of the caecum was strongly lectin-positive and here also microvillus disruption was evident. Low levels of lectins were detected on the luminal surface of the colon; no microvillus abnormalities were detected in this region.

The nutritional toxicity of Phaseolus vulgaris lectins

In rats fed on beans (Phaseolus vulgaris) the poorly digestible lectins were shown to react with intestinal cells in vivo and to cause a disruption of many of the brush borders of duodenal and jejunal enterocytes. Although depressed to a certain extent, absorption still occurred, probably through the non-disrupted cells of the small intestine. In addition, abnormal absorption of potentially harmful substances, lectin-related or of bacterial origin, could also occur, possibly as a direct effect of the disruption caused by the lectins on the enterocytes. It is suggested that toxicity was the result of ensuing systemic effects, such as for example the observed high N excretion possibly through increased tissue catabolism.

Isolectins of Phaseolus vulgaris. Physicochemical studies

By a combination of solubility fractionation, continuous free-flow high voltage electrophoresis, molecular sieve and affinity chromatography on fetuin-Sepharose 4B, several lectin fractions of different isoelectric point were obtained from the seeds of Phaseolus vulgaris cv. "Processor". The albumin isolectin range comprised of five major lectin components with isoelectric points between pH 4.6 and 5.2, while the partly overlapping globulin isolectins contained several more lectin components with higher isoelectric points. The two groups had similar amino acid and sugar composition but were only partially identical by immunochemical criteria. The isolectins were also shown to be similar by physicochemical measurements with a common protomer weight value of about 119000. Values of so20,w, 6.84 and 6.76 S, and of V av, 0.712 and 715 ml/g, for the albumin and the globulin lectins, respectively, also indicated a close similarity. Both groups contained, in a slow equilibrium with the protomer, just over 10% of dimer and oligomers. In addition, the albumin lectins also contained a small, 2 S, dissociation product in a slow equilibrium with the protomer. The hydrodynamic data obtained for the albumin isolectins: [eta] = 0.063 dl/g; beta = 2.42 . 10(6) and f/fo = 1.56 indicated a highly voluminous particle with an effective volume of 8.6 . 10(-18) ml. This type of molecular arrangement was general for the major P. vulgaris seed glycoproteins and was, thus, suggested to be of potential importance for their physiological functioning during seed maturation and germination.

Metabolism of trypsin-inhibitory proteins in the germinating seeds of kidney bean (Phaseolus vulgaris)

A number of proteins with trypsin-inhibitory activity was separated by isoelectric focusing and their amounts measured in the extracts of the seeds of kidney bean at various stages of germination up to 16 days.The total trypsin inhibitor content of the dormant seed, 2.2 mg per g bean rose to about 3.6 mg by the seventh day and declined slowly after the tenth day of germination. The individual trypsin inhibitors however, appeared to change independently of each other and some components disappeared almost completely with the progress of germination. The emergence of an inhibitor not found in the dormant seed was also observed. Some of the inhibitor proteins attained a maximum concentration by the 7-8th day of germination. This coincided with a similar maximum in the general protein and proteolytic enzyme content of the germinating bean seeds. The results obtained suggested that the main function during germination of these protein components might not be related to their trypsin-inhibitory activity.

Changes in proteolytic enzyme activities and transformation of nitrogenous compounds in the germinating seeds of kidney bean (Phaseolus vulgaris)

Hydrolytic activity towards synthetic substrates and denatured proteins was measured in the extracts of the seeds of kidney bean at various stages of germination up to 16 days.Of the peptide hydrolases, chymotrypsin-type activity was stable for the first 7 days, then rapidly increased towards the end; leucine aminopeptidase activity decreased to a minimum (8th day) then slowly increased again; trypsin-type activity remained constant throughout.Proteolytic and autodigesting activities showed an optimum between pH 5.0 and 5.5. Both activities decreased slowly first, then rose to a sharp maximum at the 8th day. The haemoglobin-digesting activity after a minimum increased again at the 14th day. The autodigesting activity had an additional maximum.Concomitant with these changes, non-protein nitrogen increased twofold by the 5th day, remained constant up to the 12th day and then increased again. Protein content on the other hand decreased first, had a maximum at the 9th day after which it steadily decreased again. The amounts of albumins and globulins changed independently of each other: albumins decreased continuously with the exception of a steady period (5-9th days), while globulins were more stable except for a sharp minimum (6-7th days) and a steady decrease after the 13th day.

Free-flow electrophoresis of proteins in phenol-containing solvents at various pH values

1. Several proteins were found to migrate when subjected to free-flow electrophoresis in buffered phenol-ethanediol-water (3:2:3, w/v/v) solvent mixtures. Mobility of these proteins changed with changing pH (apparent) values of this medium. A pH value of zero mobility for each individual protein could be estimated. 2. Founded on these observations, a high-voltage electrophoresis method in free-flowing buffer films was worked out. The method as presented here was particularly suitable for the separation of proteins on a preparative scale. Application of this and other protein fractionation techniques in dissociating media for the investigation of structural and other insoluble proteins was discussed.

The isolation of two proteins, glycoprotein I and a trypsin inhibitor, from the seeds of kidney bean (Phaseolus vulgaris)

1. The isolation of two proteins from the seeds of kidney bean is described. 2. The individual steps in the purification procedure included: extraction of the seeds at pH9.0, dialysis, first against pH9.0 and then against pH5.0 buffers, high-voltage electrophoresis of the proteins soluble at pH5.0 and chromatography on Sephadex G-200, Sephadex G-75 and DEAE-Sephadex columns. 3. Of the two proteins isolated, the first and larger component was a glycoprotein and its carbohydrate part was mainly composed of d-mannose and d-glucosamine together with smaller amounts of arabinose, xylose and fucose. 4. The second protein component isolated was a trypsin inhibitor and was almost entirely devoid of sugars but contained a firmly bound pinkish-blue pigment. 5. The amino acid composition of the two proteins was determined. 6. The glycoprotein contained very little if any cyst(e)ine but was relatively rich in aromatic amino acids, whereas the trypsin inhibitor had an unusually high cystine content (nearly 15%) but was relatively poor in valine and in aromatic amino acids.

The properties of bovine serum albumin and chymotrypsinogen A in solvent mixtures containing phenol

1. The optical rotation and reduced viscosity of bovine serum albumin and chymotrypsinogen A in solvents containing phenol, acetic acid and water were studied. 2. The changes brought about in the properties of the proteins by varying the composition of the solvent or by heat treatment in these solvents were established to be reversible. 3. A method for returning the proteins to aqueous media, based on these observations, was worked out. 4. The recovered proteins were shown to be very similar to, if not identical with, the native proteins on the basis of measurements of optical rotation, viscosity, sedimentation, ultraviolet spectroscopy, immunochemical behaviour (serum albumin) and proteolytic activity (chymotrypsinogen A, after activation with trypsin). 5. The importance of the findings for partitioning of polyelectrolytes in the phenol-aqueous buffer systems is discussed.