H.A. McKenzie

Effects of milk protein genetic variants on milk yield and composition.

Effects of genetic variants of the milk proteins, alpha S1-casein, beta-casein, kappa-casein and beta-lactoglobulin (beta-lg), on milk yield and composition, particularly the protein composition, were investigated in milk samples from 289 Jersey and 249 Friesian cows in eight commercial herds. Milk protein genotypes had no significant effect on yields over a complete lactation of milk and fat, but significant differences in fat content were detected for beta-casein (B, A1B, A2 greater than A1A2) and beta-lg (B, AB greater than A) variants. Significant differences between beta-lg variants were also found with total solids (B, AB greater than A), casein (B, AB greater than A), whey protein (A greater than AB greater than B) and beta-lg (A greater than AB, AC greater than B greater than BC) concentrations. Casein genotypes were not significantly different in total protein and casein concentrations but many differences were found in casein composition. alpha S1-Casein variants significantly affected alpha S1-casein (BC greater than B) and kappa-casein (B greater than BC) concentrations. beta-Casein variants affected concentration and proportion of beta-casein (A1B, A2B greater than A1, A1A2, A2, B), alpha S1-casein (A1, A2 greater than B) and kappa-casein (B greater than A2) and concentration of whey protein (A1 greater than most other beta-casein variants). kappa-Casein variants affected concentration and proportion of kappa-casein (B greater than AB greater than A), proportion of alpha S1-casein (A greater than AB greater than B) and concentrations of beta-lg (A greater than AB, B) and alpha-lactalbumin (A, AB greater than B). Differences in milk composition were found between breeds, herds and ages, and with stage of lactation. The potential use of milk protein genotypes as an aid in dairy cattle breeding is discussed.

Effects of milk protein genetic variants and composition on heat stability of milk

Skim milk samples from 126 Friesian and 147 Jersey cows in eight commercial herds were preheated at 85 °C for 30 min and concentrated to 200 g l −1 total solids. A heat coagulation time–pH curve was determined at 120 °C for each treated sample. Heat coagulation times ranged from 1 to 50 min at the non-adjusted pH and 1 to 60 min at the pH of maximum stability. The following statistically significant effects were found. Maximum heat stability was affected by genetic variants of κ-casein (B > AB > A; P A; P AB > A; P s1 -casein and β-lactoglobulin concentrations. Milk from Jersey cows had greater maximum and natural heat stability than milk from Friesian cows. Differences were found between herds within breed for natural heat stability, but not for maximum heat stability. Maximum heat stability declined with age of the cow. The heat stability of skim milk samples taken from 40 Jersey cows in one of the herds was determined at 140 °C. A considerable variation was found in the coagulation time–pH curves. There was a difference in natural heat stability between κ-casein variants (B > AB; P s1 -casein genetic variant, age of cow, stage of lactation and concentration of γ-casein.

Porcineβ-lactoglobulin A and C

SummaryThe occurrence of the dominant ‘whey’ protein in samples of milk from 1180 sows is examined. It exhibits genetic polymorphism with some unusual features. Although immunologically different from bovine β-lactoglobulin, it is shown by chemical studies of the isolated protein to be a β-lactoglobulin. Two homozygous genetic variants, designated porcine β-lactoglobulin A and C, are isolated and their amino acid compositions and peptide maps compared. It is shown that the C variant has +1 His, −1 Gln, and +1 Asp, −1 Glu, with respect to the A variant. These variants, containingca. 162 residues per molecule, are considered in relationship to porcine β-lactoglobulins isolated by other workers. The sequence of the first 50 residues is determined and compared with sequence of the bovine protein. The sequences ofca. 70% of the remaining residues is proposed on the basis of the composition of tryptic peptides and assumed homology.

Studies on equine transferrin. I: The isolation and partial characterization of the D and R variants

Each of two genetic variants of equine transferrin, D and R, is isolated from the blood of the heterozygote by a gentle fractionation procedure at pH 7.2. It is shown by step gradient polyacrylamide gel electrophoresis at pH 7.9 that each of these phenotypes exhibits two major bands (designated F, fast, and S, slow) and several minor bands. Components corresponding to these bands are separated by ion-exchange chromatography at pH 6.6 and 6.9 respectively for the D and R variants. The F and S components of each variant contain respectively four and two sialic acid residues. The nature of their heterogeneity is, at least in part, due to their varying sialic acid contents. It has not been possible to desialylate them completely by neuraminidase. On the basis of comparative studies of the tryptic and chymotryptic peptide maps of transferrins D and R it is concluded that there are at least two amino acid substitutions--D:R:Asp:Gly and Glu:Gly. These two substitutions are qualitatively in accordance with the difference in the electrophoretic mobility between the two variants at alkaline pH.

Comparative studies of alpha-lactalbumin and lysozyme: the proteins of kangaroo (Megaleia rufa and Macropus giganteus) and horse (Equus caballus).

SummaryAs part of a study of the ‘whey’ proteins of various mammals, a comparison is made of the α-lactalbumins and lysozymes of the kangaroo and horse. In the milk of the red kangaroo (Megaleia rufa) there is only one α-lactalbumin and it occurs throughout lactation, but no lysozyme has been detected. There are two α-lactalbumins in the milk of the grey kangaroo (Macropus giganteus), one, designated α-lactalbumin Zone B, is present throughout lactation; the second, designated α-lactalbumin Zone A, is present only in late lactation. One lysozyme is also present. The milk of the horse (Equus caballus) contains one α-lactalbumin and at least one lysozyme. Partial amino acid sequences are proposed from sequence determination and from analyses of tryptic peptides compared with the known sequences of other α-lactalbumins and lysozymes.

Feline whey proteins: Identification, isolation and initial characterization of α-lactalbumin, β-lactoglobulin and lysozyme

Abstract 1. 1. Both α-lactalbumin and β-lactoglobulin-like proteins were detected in the whey fraction of feline milk by immunoblotting with rabbit antisera to α-lactalbumin and β-lactoglobulin, respectively. 2. 2. α-Lactalbumin was found to occur in both glycosylated and unglycosylated forms in approximately equal concentrations. No polymorphism of feline α-lactalbumin was found. 3. 3. Feline β-lactoglobulin-like proteins produced complex electrophoretic pattenrs that appears to be determined by three distinct loci. Between two and five genetic variants are expressed by each locus. 4. 4. Lysozyme was detected at levels of approximately 1 mg/ml in skim milk. 5. 5. The identification of the proteins as α-lactalbumin, β-lactoglobulin and lysozyme were confirmed by determination of N- terminal amino acid sequences.

The fractionation and characterization of bovine tear proteins, especially lactoferrin

SummaryGentle procedures are described for the fractionation of bovine tear fluid by a combination of centrifugation, salt precipitation, gel filtration and ion exchange chromatography. Fractions are examined by gel electrophoretic and immunological methods. Reference patterns are compiled and compared with bovine milk and serum patterns. Properties of some of the components are determined. Lactoferrin is isolated in two separate, but closely related, fractions. A nacidic protein with a molecular weight of 23 000 daltons, is also isolated. Distinct heterogeneity is observed between individual animals, suggestive of a genetic polymorphism. A method is presented for the determination of the antibacterial activity of tear fluid and its fractions.

Porcineα-lactalbumin A and B

SummaryThe occurrence of the ‘whey’ protein, α-lactalbumin, in pig (Sus scrofus) milk samples from 904 sows is examined. A semi-discontinuous buffer system has been developed to detect the existence of genetic polymorphism. There are two homozygous variants, designated A and B. Both variants are isolated and it is shown by peptide and sequencing studies that the A variant differs from the B variant by having an Arg residue substituted for the Lys residue at the N-terminus of the molecule. The sequence of the first thirty residues is determined and compared with those of related α-lactalbumins.

Haemoglobin, serum albumin and transferrin variants of bali (banteng) cattle, Bos (Bibos) Javanicus

1. Individual blood samples from 144 Bali (Banteng) cattle [Bos (Bibos) javanicus] in the Northern Territory of Australia and from 61 Bali cross cattle, were examined by zone electrophoresis to determine the variants of haemoglobin, serum albumin and transferrin that are present. 2. Of the common cattle haemoglobin variants (A and B) only variant B occurs in the Bali cattle samples. A second variant, designated CBali, occurs in Bali cattle either as the heterozygote (B CBali) or as the homozygote, the frequencies of occurrence indicating a two-allele system of inheritance without dominance. The CBali cross samples may exhibit the homozygous or heterozygous A variant. 3. The CBali variant has an electrophoretic mobility intermediate between those of the A and B variants at pH 8.6 and 9.1 but closer to B than to A (B greater than C greater than A). It appears to be similar in mobility to the C variants found in Indian Khillan (CKhillan) by Naik, Sukumaran and Sanghvi (Anim. Prodn, 1965 I, 275-277), and in Asian cattle by Oishi, Abe and Namikama (Immunogenet. Lett., 1968 5, 170-173) and Abe, Mogi, Oishi, Tanaka and Suzuki (Proc. XIIth Europ. Conf. Anim. Blood Groups Biochem. Polymorphisms 1972, pp. 225-228), but appreciably different from those in Kenyan and Rhodesian cattle (CRhodesia) found by Braend (Anim. Blood Grps Biochem. Genet., 1971 2, 15-21) and Carr (Rhod. J. agric. Res., 1964 3, 62-62A), respectively. It is also different in mobility from the C variant found by Winter, Mayr, Schleger, Dworak, Krutzler and Burger (Res. vet. Sci., 1984 36, 276-283) in the mithun.(ABSTRACT TRUNCATED AT 250 WORDS)