The term "functional potential" was introduced to better approach to the understanding of the relationships between the structure and the functional properties of food proteins. Although in practice the complex of structural features of a protein contributes to its functionality, it is very useful to regard the functional potential of the protein surface on the one side and to look on special effects of protein conformation (role of compact or unfolded state) on the functionality on the other side. This point of view may help to design the best strategy of modification of the protein structure and functionality. The special situation of the oligomeric legume storage protein, i.e. legumin-like 11 S globulins and vicilin-like 7 S globulin, and the structural and functional modification of 11 S globulin by limited tryptic hydrolysis and by acylation are discussed in this paper.

The influence of various levels of succinylation on the structure of the legumin from pea seed has been studied by the techniques of sedimentation velocity, viscometry, fluorescence and circular dichroism spectroscopy, as well as dynamic light scattering. The protein dissociates gradually into the 3s subunit forming a 7s intermediate. At a level of 75 -80% succinylation, sudden unfolding of the protein occurs characterized by drastic changes in viscometric and spectroscopic properties. The fluorescence spectra point to the formation of a novel organized structure at a moderate degree of modification before the molecular unfolding takes place.The succinylated subunit was shown to have a sedimentation coefficient of 3.2S, a diffusion coefficient of 5.03 x cm2 . s p l a Stokes' radius of 4.24 nm, a partial specific volume of 0.703 ml/g, an intrinsic viscosity of 0.13 dl/g, a molar mass of 52.2 kDa and a frictional ratio of 1.74.Legumin is one of the main storage proteins in the seeds of pea (Pisum sativum L.). It belongs to the group of the socalled l l S globulins, having sedimentation coefficients between lls and 14S, and molecular masses between 300 kDa and 400 kDa [l]. These proteins possess an oligomeric structure characterized by an arrangement of six subunits (3s components) [2 -41. The molecular mass of pea legumin was reported by different authors to be in the range 330 -410 kDa [l, 5, 61. By means of small-angle X-ray scattering, a value of 359 f 25 kDa was obtained [7]. Disulphide-bonded polypeptide pairs with molecular mass 54 kDa constitute most of the 3s subunit of the legumin [8]. In addition, polypeptide pairs varying in molecular mass over 35-58 kDa have been observed which associate in various ways to give rise to different molecular forms of legumin IS].Due to very similar quaternary structures [9, lo], the 11s plant proteins show an analogous behaviour dissociating into subunits [l 11. Therefore, the decay of oligomeric structure by an increase of negative charge caused by succinylation effects similar changes in the structure of different 11s proteins. Although there are specific differences in the dissociation behaviour of the peanut [12], sunflower seed [13] and rape seed [14] 11s globulins, a step-by-step decay of the native structure, and a marked change in conformation at a critical step of succinylation, were observed in each case.The present paper deals with the effect of succinylation on the oligomeric structure of the 11s globulin (legumin) from pea. Structural changes of the protein were followed using ultracentrifugation, viscometry, circular dichroism and fluorescence spectroscopy. The physicochemical properties of the dissociation products, including molecular mass and shape, were investigated by a combination of hydrodynamic methods, including dynamic light scattering. MATERIALS AND METHODSLegumin was isolated and purified according to Gueguen et al. [15]. Lyophilized preparations containing small amounts of aggregated material were purified additionally by gel filtration on a ...

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The 12 S globulin of rapeseed represents an oligomeric protein with a molecular weight of 300,000. It is composed of 6 subunits, which are arranged in a trigonal. antiprism with the point group symmetry 32 (D3).Each subunit contains smaller units (polypeptide chains) with molecular weights in the range of 18,500 to 31,000. The protein contains the following 4 polypeptide chains differing by their molecular weights in the SDS-electrophoresis: 18,500 k 800, 21,100 500, 26,800 900, 31,200 k 1,600.According to its quaternary structure the protein dissociates under milieu conditions : low ionic strength extremely high or low pHThe secondary structure of the protein is characterized by a low (1 1 yo) content of a-helix and a relatively high (31 %) content of &conformation.11/12 S globulins in the seeds of different plant species and botanical families.Owing to its structure and physico-chemical properties the rapeseed protein is closely related to otherThe 12 S globulin represents a main storage protein in the seeds of Brassica species [I -61. 21-33% of the nitrogen in sodium chloride extracts of defatted rapeseed varieties or 18-28The globulin was first isolated by BHATTY et al.[I] from oil-free rapeseed meal by extraction with 10 % sodium chloride, precipitation by dialysis against water, and chromatographic separation on Sephadex G-100. SIMARD et al. 191 used the technique of fractionating precipitation and dissolution by ammonium sulphate for the isolation of the protein. SCHWENKE et al. [lo] described a combined gel and ionic-exchange chromatographic purification of the 12 S globulin. The present paper summarizes the results of research on the physico-chemical properties and structure of the 12 S globulin of rapeseed. of the total seed nitrogen correspond to this protein [l, 7, 81. Hydrodynamic properties and molecular weightAfter isolation and purification of the protein BHATTY et al.[l] could show by ultracentrifugal analysis that this rapeseed globulin, owing to its sedimentation property, corresponds to the group of 11/12 S seed proteins. The authors found a sedimentation coeffi-

The 11-S globulin from sunflower seed has a radius of gyration R, of 3.95 nm and a maximum dimension L of 11 .O nm. For the 1 1-S globulin from rape seed R, and L amount to 4.1 nm and 11.2 nm, respectively. Both molecules have an almost spherical shape with slightly differing dimensions. Both molecules consist of six subunits arranged as a trigonal antiprism with dihedral point group symmetry 32.The so-called 11-S globulins are oligomeric proteins with sedimentation coefficients between 10.8 S and 14.6 S and molar masses between 3.0 x lo5 g/mol and 4.0 x lo5 g/mol [l]. Apart from the 7-S globulins, they are the main storage proteins of the seed of various plant species.The sedimentation coefficients of the 11-S globulins from sunflower seed (Heliunthus unnuus L.) and rape seed (Brassica nupus L.) amount to 11.8 S and 12.7 S, the molar masses to 3.05 x lo5 g/mol and 3.0 x lo5 g/mol, respectively [2,3]. According to electron microscope investigations, both these 1 I-S globulins have a diameter of 8 -10 nm and are almost spherical in shape [4,5]. Schwenke et al. [2] determined for rape globulin from hydrodynamic data a frictional ratio offif0 =1.28, which could be caused either by hydration for a spherical shape, or by a non-spherical shape.Like other 11 -S globulins the two proteins dissociate into subunits according to the following scheme [l, 61 : 11-S+2 x 7-S+6 x 3-S+12 x 2-S.Whereas the dissociation of the 11-S globulins into the 7-S subunits is dependent on ionic strength and pH, they dissociate into 2-S subunits, in most cases, only in the presence of urea or guanidine hydrochloride. Thus, it is an open question whether the 11-S globulins consist of six or twelve subunits.In the present paper the molecular parameters of the 11-S globulins from sunflower and rape seed have been determined by means of small-angle X-ray scattering and compared with each other. The scattering curves of the two globulins have been compared with theoretically calculated scattering curves of different models, and structural models for the overall shape and the quaternary structure of the two 1 I-S globulins have been derived.(1) MATERIALS A N D METHODSThe 11-S globulins from sunflower and rape seed were prepared according to Schwenke et al. [7,8]. Both proteins were studied in 0.05 M Tris buffer, p H 8.0,0.25 M NaC1. The small-angle X-ray scattering was measured on three protein solutions with concentrations ranging from 6 g protein) to 25 g protein/l.The measurements were performed using an automated Kratky diffractometer (Anton Paar KG, Austria) or an automated four-slit diffractometer (a completely reconstricted Rigaku-Denki M2 model, Japan). A highly stabilized Xray generator (VEB Freiberger Prazisionsmechanik, GDR), equipped with a 1.4-kW copper tube, was used. Registration of the scattered radiation was done with a proportional counter or a scintillation counter. The protein samples were kept in thin-walled glass capillaries having a diameter of 1 mm. The measurements on the Kratky diffractometer and four-slit diffractomet...