DAIRY CHEMISTRY AND BIOCHEMISTRY B-Lg also binds free fatty acids and thus it stimulates lipolysis(lipases are inhibited by free fatty acids ); perhaps this is its physiological function. BSA also binds hydrophobic molecules, including fatty acids; perhaps BSa serves a similar function to B-lg in those species lacking B-lg 4.78 Denaturation Denaturation of whey proteins is of major technological significance and will be discussed in Chapter 9 4.8 a-Lactalbumin a-Lactalbumin(a-la)represents about 20% of the proteins of bovine whey (3.5% of total milk protein) it is the principal protein in human milk. It is a small protein with a molecular mass of c. 14 kDa. Recent reviews of the literature on this protein include Kronman( 1989) and Brew and Grobler (1992) 4.8.1Am The amino acid composition is shown in Table 4. 4. a-La is relatively rich in tryptophan(four residues per mole. It is also rich in sulphur(1.9%)which is present in cystine (four intramolecular disulphides per mole) and me- thionine; it contains no cysteine(sulphydryl groups). The principal -la's in no phosphorus or carbohydrate, although some minor forms may in either or both. The isoionic point is c. pH 4.8 and minimum solubility in 0.5 M NaCl is also at pH 4.8 4.8.2 The milk of Western cattle contains only z- la b but Zebu and Droughtmas- ter cattle secrete two variants, A and B a-La A contains no arginine, the one Arg residue of a-la b being replaced by glutamic acid 4.8.3 Primary structure The primary structure of a-la is shown in Figure 4.25. There is considerable homology between the sequence of a-la and lysozymes from many sources The primary structures of a-la and chicken egg white lysozyme are very similar. Out of a total of 123 residues in a la, 54 are identical to correspond ing residues in lysozyme and a further 23 residues are structurally similar (e.g. Ser/Thr, Asp/ Glu)192 DAIRY CHEMISTRY AND BIOCHEMISTRY /I-Lg also binds free fatty acids and thus it stimulates lipolysis (lipases are inhibited by free fatty acids); perhaps this is its physiological function. BSA also binds hydrophobic molecules, including fatty acids; perhaps BSA serves a similar function to p-lg in those species lacking D-lg. 4.7.8 Denaturation Denaturation of whey proteins is of major technological significance and will be discussed in Chapter 9. 4.8 or-Lactalburnin a-Lactalbumin (a-la) represents about 20% of the proteins of bovine whey (3.5% of total milk protein); it is the principal protein in human milk. It is a small protein with a molecular mass of c. 14kDa. Recent reviews of the literature on this protein include Kronman (1989) and Brew and Grobler (1992). 4.8. I Amino acid composition The amino acid composition is shown in Table 4.4. a-La is relatively rich in tryptophan (four residues per mole). It is also rich in sulphur (1.9?40) which is present in cystine (four intramolecular disulphides per mole) and me￾thionine; it contains no cysteine (sulphydryl groups). The principal a-la’s contain no phosphorus or carbohydrate, although some minor forms may contain either or both. The isoionic point is c. pH 4.8 and minimum solubility in 0.5 M NaCl is also at pH 4.8. 4.8.2 Genetic variants The milk of Western cattle contains only r-la B but Zebu and Droughtmas￾ter cattle secrete two variants, A and B. a-La A contains no arginine, the one Arg residue of a-la B being replaced by glutamic acid. 4.8.3 Primary structure The primary structure of a-la is shown in Figure 4.25. There is considerable homology between the sequence of a-la and lysozymes from many sources. The primary structures of r-la and chicken egg white lysozyme are very similar. Out of a total of 123 residues in r-la, 54 are identical to correspond￾ing residues in lysozyme and a further 23 residues are structurally similar (e.g. Ser/Thr, Asp/Glu)