Aust. J. Bioi. Sci., 1981, 34, 149-59 Bovine a-Lactalbumin C and aS1 -, p- and K-Caseins of Bali (Banteng) Cattle, Bos (Bihos) javanicus K. Bell/ K. E. Hopper, B.C and H. A. McKenzieB,D A Department of Physiology, University of Queensland, St. Lucia, Qld 4067. B Department of Physical Biochemistry, John Curtin School of Medical Research, Australian National University, P.O. Box 334, Canberra City, A.C.T. 2601. C Present address: Kolling Institute of Medical Research, Royal North Shore Hospital, St. Leonards, N.S.W. 2065. D Address for reprints. Abstract An electrophoretic examination is made of milk samples taken from eight Bali (banteng) cattle, Bos (Bibos) javanicus, at Beatrice Hills, Northern Territory, Australia. Starch-gel electrophoresis at pH 8· 5 (NaOH-H3B03 buffer) and filter-paper electrophoresis at pH 8· 6 (diethylbarbiturate buffer) indicate that all samples contain a new a-lactalbumin variant, designated a-lactalbumin C. The order of mobility for bovine variants is A > B > C. The C variant differs from the common B variant in having one more amide residue (substitution of Asn for Asp or GIn for Glu). Examination of milk samples by urea-starch-gel electrophoresis at alkaline pH indicates that there is a new asrcasein variant, designated as1-casein EBol;, present in some samples. No new K-casein variant is detected by this method (all samples typing as K-casein B). A new variant of jJ-casein, designated A4, is detected by urea-starch-gel electrophoresis at low pH. The variants of milk proteins observed in this paper and in Bell et al. (1981) are discussed in relation to those of other members of the Bovinae, especially the yak, Bos (Poephagus) grunniens. Introduction In the paper by Bell et al. (1981) we have examined samples of milk taken from eight Bali (banteng) cattle, Bos (Bibos) javanicus, at the Beatrice Hills Experiment Station, Northern Territory. It was shown that f)-lactoglobulin is the dominant whey protein present and that it occurs as three new variants, designated f)-lacto­ globulin E, F and G. In the course of this work it was noticed that there was a prominent band due to a-lactalbumin, moving more slowly than bovine a-lactalbumin B of Bos taurus or the A variant of Bos indicus. The isolation and characterization of this new variant, designated a-lactalbumin C, is described in the present paper. Attention is also given to the variants of as1 -' f)- and K-casein. Two new variants, as1-casein EBaJi and f)-casein A 4 are detected. In the light of these studies on the milk proteins of the subgenus Bos (Bibos) javanicus and the work of Grosclaude et al. (1976) on those of the subgenus Bos (Poephagus) grunniens, it is possible to compare the variants of the proteins of these subgenera to the known variants of the subgenus Bos and to those of the genus Bubalus, and consider their evolution. Materials and Methods These were similar to those used by Bell et al. (1981), with the following additions. Filter-paper electrophoresis of total 'whey' protein was performed according to the method of Aschaffenburg and Drewry (1955). Urea-starch-gel electrophoresis in alkaline solution was performed as described by Aschaffenburg and Thymann (1965). jJ-Caseins were further typed in acid solution (formic 150 K. Bell, K. E. Hopper and H. A. McKenzie acid buffer, pH 3'0) by the method of Bell described by McKenzie (1971, p. 500). Starch-gel electrophoresis of a-lactalbumin fractions was performed with the semi-discontinuous buffer system of Ferguson and Wallace (1963). Results Electrophoretic Typing of rx-Lactalbumin All skim milk samples of the eight Bali (banteng) cows were examined by the starch-gel electrophoresis procedure for typing f3-lactoglobulin, as described by Bell et al. (1981), and showed a single rx-lactalbumin band, moving more slowly than the A and B variants (see Fig. 1 of that paper). This band had a lower mobility than bovine serum albumin in this buffer system, whereas the A and B variants had a higher mobility than bovine serum albumin. That the protein in the band was an rx-lactalbumin was confirmed by immunoelectrophoresis in which a single arc was formed with rabbit antiserum to bovine rx-lactalbumin B. Also, the new protein and rx-lactalbumin A and B showed immunological identity on immunoelectrophoresis with rabbit antiserum to the B variant. The new variant has been designated rx-lactalbumin C. The C variant also showed a single band moving more slowly than the A and B variants on filter-paper electrophoresis at pH 8· 6 (Fig. 1). Isolation of rx-Lactalbumin C A sample of ammonium sulfate total whey protein from cow 171 was dialysed against 0'OS6M Tris-O·OSM HCl buffer, pH 7·8, and SUbjected to gel filtration on Sephadex G7S. The elution profile was similar to that of Fig. 2 in Bell et al. (1981). The minor fraction 4 exhibited two bands on electrophoresis. They were of lower mobility than the main rx-lactalbumin C fraction. These bands probably represent components analogous to the minor glycoprotein components isolated from fraction 4 during studies of bovine rx-lactalbumin A and B (Hopper and McKenzie 1973). They have not been studied further in the present work. Fraction S (Bell et al. 1981) contained the main rx-lactalbumin C component, as well as a minor band analogous to the fast component (FC) of rx-lactalbumin A and B (Hopper and McKenzie 1973). This fraction was concentrated by ultrafiltration and subjected to ion-exchange chromatography on DEAE-Sephadex ASO in the Tris-HCl buffer and eluted with a linear NaCl gradient. The elution profile showed one major peak (the main rx-lactalbumin C component), followed by two minor peaks. The first minor peak was probably a reflection of apparent heterogeneity (Hopper 1973) and the second minor peak was component FC of rx-lactalbumin C. The mobility of the latter component was similar to that of the main component of bovine rx-lactalbumin B on electrophoresis in the Ferguson-Wallace system. It will be recalled that, in turn, FC of rx-lactalbumin B has the same mobility as the main component of rx-lactalbumin A (Hopper and McKenzie 1973). Electro­ phoretic patterns of the variants A, Band C are compared in Fig. 2 of the present paper. The elution volume of rx-lactalbumin C on gel filtration was the same as that for the B variant, and since it does not contain carbohydrate (see below), it probably has a similar molecular weight to that of rx-lactalbumin B (c. 14000). IX-Lactalbumin C of Bali Cattle 151 Fig. 1. Paper electrophoretic patterns of concentrated 'whey' protein solutions in diethylbarbiturate buffer, pH 8·6, ionic strength 0·05. (a) Droughtmaster: j1-lactoglobulin BDr and IX-lactalbumin AB; (b) Bali (banteng): j1-lactoglobulin EF and IX-lactalbumin C. Fig. 2. Starch-gel electrophoretic patterns of IX-lactalbumin variants in Ferguson-Wallace semi­ discontinuous buffer system. FC, ",-lactalbumin C, fast component; C, IX-lactalbumin C at two different concentrations; B, IX-lactalbumin B; A, IX-lactalbumin A. Fig. 3. Alkaline urea-starch-gel electrophoretic patterns, Aschaffenburg-Thymann system, showing casein types in skim milk samples. (a) Bali cow: IX-slcasein CE, p-casein A, K-casein B; (b) Drought­ master: IX'I-casein BC, j1-casein A, K-casein A; (c) Bali: iXsl-casein CE; j1-casein A; K-casein B; (d) Droughtmaster: ocu-casein BC, B-casein A, K-casein B; (e) Bali: "'sl-casein CE, p-casein A, K-casein B; (f) Droughtmaster: IX'I-casein BC, j1-casein AB, K-casein B. j1-lactoglobulins A, B and Droughtmaster migrate just ahead of the j1-casein bands in patterns (b), (d), and (f). Fig.4. Acid urea-starch-gel electrophoretic patterns of skim milk samples (system of Bell). (a) Bali: p-casein A4; (b) Droughtmaster: p-casein At,A2; (c) Bali: j1-casein A2; (d) Droughtmaster: j1-casein BA 2. 152 K. Bell, K. E. Hopper and H. A. McKenzie Amino Acid Analysis and Peptide Maps Initial amino acid analyses of the main component and fast component (FC) of a-lactalbumin C are presented as set 1 in Table 1. There is no apparent difference in the analyses. This is accordance with expectation if the FC and main components of the C variant are related to one another in the same way as the FC and main components of each of the previously studied variants (A and B) are related to one another. In these variants FC differs from the main component in having one less amide residue per molecule: such a difference would not be detected in amino acid analysis (Hopper and McKenzie 1973). No humin formation was observed in the hydrolysates and no hexosamines were detected in the analyser elution profiles. Hence it would appear that neither component contains a carbohydrate moiety. Table 1. Amnio acid analysis of bovine a-lactalbumin variants C (fast component), C, B and A Results are expressed as moles per mole protein. n.d., not determined Residue Set lA Set 2B Variant C Variant C Variant C Variant B Variant A (fast component) (main component) Lys 13·0 12·9 12'1 12·1 12·3 His 2·9 2·9 3·0 2'5 2·6 Arg 0·9 0·8 1·0 1·0 0 Asp 20·8 21·2 20·6 20'5 20·8 Thr 6·8 6'7 6·8 6·8 6·8 Ser 6·2 5·9 6·8 6·9 7·0 Glu 12·6 12'8 12·9 13 ·1 14·4 Pro 2'3 1'7* 2·1 2·1 2·2 Gly 6 6 6 6 6 Ala 3·2 2·8 3·3 3·0 3·4 1-Cys 7'8* Val 5·4 5·6 5·8 5·8 5·8 Met 0·8 0·8 0·9 0·9 1·0 lie 7·3 7·6 8·0 8·1 8·2 Leu 12'3 12·6 13 ·1 13·3 13·3 Tyr 3·5 3·6 3·9 4·1 3·9 Phe 3·6 3·7 4'0 4·0 4·1 Trp n.d.