Cystine lactoglobulin

Whey proteins /8-Lactoglobulin 8-17 18,205-18,363 5.35-5.49 Globular protein, containing one cysteine and two cystine residues Formation of dimers in pH range 5.2-7.5 octamerization may occur at pH 3.5-5.2... 

Figure 2. SDS gel electrophoresis of the products of partial cystine cleavage for several test proteins. A. molecular weight standards, B. yeast alcohol dehydrogenase. C. P-lactoglobulin, D. hen egg lysozyme, E. ovalbumin, F. calf fetal serum fetuin. Molecular weight standards are indicated by arrows on the left side of the gel and are bovine serum albumin (66,300), bovine liver glutamate dehydrogenase (55,400), porcine muscle lactate ddiydiogenase (36,500), bovine erythrocyte carbonic anhydrase (31,000), soybean trypsin inhibitor (21,500), hen egg lysozyme (14,400), bovine lung aprotinin (6,000), unresolved bovine pancreatic insulin A and B chains.

Casein is low in sulphur (0.8%) while the whey proteins are relatively rich (1.7%). Differences in sulphur content become more apparent if one considers the levels of individual sulphur-containing amino acids. The sulphur of casein is present mainly in methionine, with low concentrations of cysteine and cystine in fact the principal caseins contain only methionine. The whey proteins contain significant amounts of both cysteine and cystine in addition to methionine and these amino acids are responsible, in part, for many of the changes which occur in milk on heating, e.g. cooked flavour, increased rennet coagulation time (due to interaction between /3-lactoglobulin and (c-casein) and improved heat stability of milk pre-heated prior to sterilization. 

Similar effects are found in solutions of some, but not all, proteins. Thus horse hemoglobin (Richards, 177) and j3-lactoglobulin (E. J. Cohn, J. D. Ferry, and M. H. Blanchard, unpublished studies, quoted in ref. 39, Chapter 24 Gronwall, 85) become decidedly more soluble in the presence of glycine. The relative solvent effect of glycine on these two proteins, and on cystine, asparagine and glycine is shown in Fig. 7 ... 

Fig. 7. Relative effects of sodium chloride (Fig. 7a) and glycine (Fig. 7b) on the solubiiity of certain proteins and amino acids. Note differences in scale of both abscissa and ordinate in Figs. 7a and 7b. In each figure, the steepest curve is for /3-lactoglobulin, then below in des ding order horse carboxyhemo obin, cystine, aspaia e, glycine.

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