Pig beta-lactoglobulin I (Sus scrofa domestica, Artiodactyla). The primary structure of the major component.

beta-Lactoglobulins from pooled milk (Sus scrofa domestica) are isolated and characterized. The complete primary structure of the major beta-lactoglobulin component I is presented. The amino-acid sequence was elucidated by automated Edman degradation of tryptic peptides and cyanogen bromide cleavage products in a liquid phase sequencer. The tryptic and cyanogen bromide peptides were separated by reverse-phase (RP-2) or size exclusion (TSK 2000 SW) high performance liquid chromatography. Pig beta-lactoglobulin is composed of only 159 amino acids in contrast to other beta-lactoglobulins which contain 162 or 166 amino acids. Sequence alignment with previously sequenced beta-lactoglobulins was obtained by introducing two gaps at positions 115 and 151-152. Thus bovine beta-lactoglobulin A reveals 62 amino-acid substitutions. The phylogenetic distance from horse beta-lactoglobulin I and II is indicated by 49.4% and 62% amino-acid exchanges, respectively. Pig beta-lactoglobulin is a mixture of two chains with Gln or Thr at position 119. The free thiol group is localized at position 59. The structural and functional aspects of beta-lactoglobulins and its role in vitamin A (retinol) transport are discussed.

The amino-acid sequence of beta-lactoglobulin II from horse colostrum (Equus caballus, Perissodactyla): beta-lactoglobulins are retinol-binding proteins.

beta-Lactoglobulin isolated from horse colostrum is heterogeneous and contains two components: beta-lactoglobulin I and beta-lactoglobulin II. These two proteins are monomeric and show differences in their electrophoretic mobilities, chain lengths and primary structures. The complete amino-acid sequence of beta-lactoglobulin II was determined by automated Edman degradation of the intact protein and of the peptides derived from these by digestion with trypsin or chymotrypsin and by chemical cleavage with cyanogen bromide. Unlike other beta-lactoglobulins which contain 162 amino acids, horse beta-lactoglobulin II is unique in that it contains 166 amino acids. The additional four amino acids represent an insertion between positions 116 and 117 of other beta-lactoglobulins so far sequenced, including horse beta-lactoglobulin I. Sequence comparison of beta-lactoglobulins I and II from horse colostrum reveals 48 amino acid substitutions (30%). Such a diversity between members of the beta-lactoglobulin gene family has not been encountered before. Sequence comparison with bovine beta-lactoglobulin A shows 85 amino acid replacements accounting for 53% of the residues. The structural homology with human retinol-binding protein may reveal similar biological functions and clues to the origin of milk proteins.

Homology between the primary structures of beta-lactoglobulins and human retinol-binding protein: evidence for a similar biological function?

Two types of beta-lactoglobulins were identified and isolated from horse colostrum: beta-1g I and beta-1g II. The amino-acid sequence of some tryptic peptides from the new monomeric beta-lactoglobulin II was determined and aligned to the other beta-lactoglobulins of known sequence and to the human plasma retinol-binding protein. The comparison of the primary structures of beta-lactoglobulins and human retinol-binding protein shows an unexpectedly high homology of 25%. We found 37 identities among 149 possible homologous residues. Among them is a tryptophan residue at position 19 of beta-lg which might represent the binding site of beta-ionone. These data suggest a common origin of beta-lactoglobulin and human retinol-binding protein and imply that beta-lactoglobulins may be involved in the metabolism of retinol.

The primary structure of monomeric beta-lactoglobulin I from horse colostrum (Equus caballus, Perissodactyla).

beta-Lactoglobulin-like proteins were detected in horse colostrum and normal milk using immunological techniques. In contrast to the beta-lactoglobulins sequenced so far these proteins are monomeric and genetically not homogenous. In this paper we report the first primary structure of a monomeric beta-lactoglobulin from horse colostrum. By means of an automatic liquid-phase sequenator the sequence of peptides obtained by tryptic digestion and by cyanogen bromide cleavage was determined. A limited tryptic digestion and hydrolysis with chymotrypsin provided the necessary overlapping peptides. The horse beta-lactoglobulin I consists of 162 amino acids, among these four cysteine, six methionine residues and one tryptophan residue. Homologous comparison with bovine beta-lactoglobulin A shows an unexpectedly great difference of 72 amino acids (or 44%). Thirteen of these exchanges are explained as two-point mutations. We found that the free thiol group, localized at position 121 or in equal amounts at positions 119 and 121 in bovine beta-lactoglobulin, is absent in beta-lactoglobulin I from horse colostrum. In position 121 a tyrosine substitution for cysteine was found. The amino-acid exchanges of the horse beta-lactoglobulin I as compared to the other beta-lactoglobulins are discussed.

The primary structure of the beta-lactoglobulin of the waterbuffalo (Bubalus arnee).

The complete amino acid sequence of the beta-lactoglobuline of the waterbuffalo (Bubalus arnee) was established. The sequence of peptides obtained by cleavage with BNPS-Skatole, CNBr and trypsin were determined automatically by the help of the sequenator. Only two differences were found in the beta lactoglobulin of the waterbuffalo compared with the bovine beta-lactoglobulin B.

beta-lactoglobulins in the mammary secretions of camel (Camelus dromedarius) and she-ass. Immunological detection and preliminary physico-chemical characterization.

The mammary secretions of a monogastric, the ass, and those of a Tylopode, the camel (camelus dromedarius), were examined by double diffusion in agarose gel against rabbit sera anti-bovine beta-lactoglobulin. Clear precipitin reactions were obtained. After immunoelectrophoresis the camel and she-ass beta-lactoglobulins showed very different electrophoretic mobilities.

Immunochemical studies on beta-lactoglobulins. precipitin reactions of sow's and mare's mammary secretions against anti - bovine beta - lactoglobulin antiserum.

By double diffusion in agarose gel, in well defined experimental conditions, cross reactions were observed between porcine beta-lactoglobulins and anti-bovine beta-lactoglobulin antisera. The immunological reactivity between these beta-lactoglobulins from a monogastric and the ruminant anti beta-lactoglobulin antiserum thus implies a certain degree of similarity between the monomeric beta-lactoglobulins examined and the dimeric of the ruminants. With the same antisera it also proved possible to demonstrate the presence of beta-lactoglobulins in the mammary secretions of another monogastric, namely, the mare. Identity reactions observed between sow's and mare's beta-lactoglobulins seem to indicate a close similarity in their structures.

Immunological evidence of beta-lactoglobulins in human colostrum and milk.

Over thirty specimens of breast milk and colostrum were examined by the double diffusion method in agarose gel using antibovine beta-lactoglobulin antisera. Cross reactions were obtained showing the presence of beta-lactoglobulins in human milk and colostrum; the strength of these reactions was comparable with those already observed with porcine and equine mammary secretions. Identity reactions were obtained between human and sow's milk against anti-bovine beta-lactoglobulin antisera. Results are discussed from the immunological and structural point of view.