Isolation, partial characterisation, and amino acid sequence of alpha-lactalbumin from platypus (Ornithorhynchus anatinus) milk.
alpha-Lactalbumin was isolated from the whey fraction of platypus (Ornithorhynchus anatinus) milk by successive ion-exchange, hydrophobic interaction and gel-permeation chromatography. The purified protein modified the action of partially-purified galactosyltransferase from platypus milk to promote the synthesis of lactose, but had very little modifier effect on bovine galactosyltransferase. Platypus alpha-lactalbumin has 126 amino-acid residues (molecular mass about 14.3 kDa), including a three-residue insertion not found in other alpha-lactalbumins or c-type lysozymes. It appears to have two sites of post-translational modification, of which at least one is N-glycosylated, to give an apparent molecular mass of 23 kDa on SDS-PAGE. The platypus sequence shows a high degree of positional identity (41-48%) with the alpha-lactalbumins of other species. Although it has no lysozyme activity, platypus alpha-lactalbumin is more similar to mammalian lysozymes than is any eutherian or marsupial alpha-lactalbumin, suggesting that this monotreme protein has evolved more slowly than other alpha-lactalbumins.
Shaw
D C
DC
Protein Biochemistry Group, John Curtin School of Medical Research, Australian National University, Canberra.
Messer
M
M
Scrivener
A M
AM
Nicholas
K R
KR
Griffiths
M
M
D000595:Amino Acid Sequence; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007768:Lactalbumin / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D008892:Milk / Q000737:chemistry*; D008969:Molecular Sequence Data; D010987:Platypus; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
D007768:Lactalbumin