The amino acid sequence of equine alpha-lactalbumin.

The article presents the determination of the amino acid sequence of equine alpha-lactalbumin, a protein from horses, using an automatic sequencer.

Identification and Composition of Equine Alpha-Lactalbumin

• The researchers have identified the sequence of amino acids in equine alpha-lactalbumin, a form of protein specifically found in horses. This protein plays a significant role in lactose synthesis in milk-secreting cells.
• This sequence comprises 123 amino acids and has a molecular weight (Mr) of 14218. In other words, there are 123 distinct ‘building blocks’ linked together to form the entirety of this protein, and its total mass is 14218 atomic mass units.

Methods of Sequence Determination

• The process of ascertaining the sequence and number of these amino acids involved several steps. Firstly, the researchers analysed the ‘native’ (unaltered) protein for the first 32 amino acid residues.
• They then exposed the protein to cyanogen bromide, a reagent often used to cleave proteins into smaller fragments. The sequence of these fragments was subsequently determined. This method provides an additional layer of analysis, confirming the sequence of the native protein and shedding light on the arrangement of residues that follow the intial 32.
• The research also utilized three types of proteolytic enzymes, molecules that can break down proteins into their component parts. These were trypsin, chymotrypsin, and Staphylococcus aureus V8. The resultant peptides (short chains of amino acids) were independently sequenced, further aiding in the overall determination of the equine alpha-lactalbumin amino acid sequence.

Comparison to Other Alpha-Lactalbumins

• In the process, researchers found that about 67% of the equine alpha-lactalbumin’s residues are identical to those found in bovine alpha-lactalbumin B, a version of the protein found within cattle. This indicates a substantial level of biological similarity between these two species regarding this particular protein.
• It was also noted there is a close homology (similarity in structure) between the equine alpha-lactalbumin and that found in other species, suggesting a conserved evolutionary role for this protein.