7 S Globulins

In the starch-SP isolate dispersions, the starch continuous network was formed first as a result of its lower transition temperature. Because the denaturation temperature of 7 S globulin was close to the gelatinization temperature of com starch, the diffusion and aggregation of amylose molecules and the swelling of starch granules was a little bit... 

The investigation of maleylated vicilin, the 7-S-globulin from faba beans, revealed the existence of a critical degree of modification for the unfolding of this type of protein, too [57]. While no significant changes in denaturation temperature and enthalpy of denaturation were found up to 63% modification, these values decrease signifi-... 

Soybean 7 S globulin has similar properties, as illustrated in Fig. 16.1. Hence, its molecular weight is also strongly dependent on pH and ionic strength. 

The amino acid compositions of both major soybean proteins, with the exception of methionine, are very similar (Table 16.10). However, large differences exist in their carbohydrate contents. The 7 S globulin contains 5% carbohydrate and the 11 S globulin less than 1% carbohydrate. 

Fig. 16.2. Soybean globulin as an emulsifier. (According to Aoki et al., 1980). The capacity of an o/w-emulsion after addition of 11S globulin (-0-) and 7 S globulin (- -) is plotted versus pH...

In the pH range of 4-10, the 7 S globulin is a better emulsifier than the 11 S globulin, when the capacity (Fig. 16.2) and the stability of an o/w emulsion are compared. Partial acid hydrolysis improves the emulsifier properties. 

Table 16.8. Amino acid sequences of subunits of the 7 S globulins, 1) 3-conglycinin a Glycine max), 2) phase-olin Phaseolus vulgaris) and 3) vicilin (Pisum sativum)...

Table 16.9. Amino acid sequences in the vicinity of the a/P cleavage site (239/240 in Table 16.8) and the P/y cleavage site (376/377 in Table 16.8) of subunits of various 7 S globulins (- space to maximize the homology)...

A great number of proteins have been purified on Sephadex G-75 (Bjork and Porath, 1959 Hanson and Johansson, 1960 Pr aux and Lontie, 1961 Bjork, 1961 Palmstierna, 1961 Ames et al., 1961 Pettersson et al., 1962). Considerably improved gel types have been introduced recently thanks to pioneering work by Flodin. These gel substances, named Sephadex G-lOO and G-200, are produced in the form of spherical beads. They can be packed in beds with excellent filtering properties this is particularly true for G-100. The behavior of serum proteins has been studied by Flodin and Killander (1962). As is seen in Fig. 6, 7 S and 19 S 7-globulins can be separated on Sephadex G-200. 

Fig. 6. Fractionation of proteins in 50 ml of human plasma on Sephadex G-200. Eluent, 0.1 M Tris + 1 M NaCI, pH 8.0 elution rate, 68 ml/hour column size, 7 X 50 cm absorption measured with LKB Uvicord recorder. Region A contains /32m-(19 S 7-) and asM-globulins, a- and /3-lipoproteins, and fibrinogen B, 7 S 7-globulin C, transferrin and D, albumin. (Flodin, 1962.)...

The variation of precipitation as a function of pH is related to the different precipitation profiles of the two protein fractions, 7 S and 11 S [97]. According to Thanh and Shibasaki [97], protein concentrations (up to 4%) are favorable for the separation of the two globulin fractions. They noted that the 7 S fraction is not very sensitive to an increase in protein concentration, whereas the 11 S fraction started to precipitate earlier with a higher protein concentration. This correlates with the large change in soluble protein observed for pH 6, a point close to the isoelectric point of the 11 S fraction and the inflection point of the protein solubility curves. The electroacidification process influences the precipitation curve of the 11 S fraction the electroacidified 11 S fraction precipitation curve presents a slight shift in comparison with the chemical acidification curves (Figure 21.15a and 21.15b). The lower precipitation for the electroacidified proteins is the result of the lower extent of precipitation obtained for the 11 S fraction [88]. 

IgG globulins, being 7 S in size, are distributed readily throughout the body fluids (50% are extravascular), and some 2-3 g are turned over daily. 

These globulins show a raipd turnover, 3 days, FOR 37%, with a distribution similar to IgM despite their 7 S size (R9). 

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