A new bovine β-casein genetic variant characterized by a Met93→Leu93 substitution in the sequence A2

Abstract

A new variant of bovine β-casein was isolated from individual milk and characterized. It is proposed for nomenclature as β-CN H. The variant H differed from the variant A2 by the substitution of the residue methionine at position 93 by a leucine residue, by the substitution of the residue glutamine at position 72 by a glutamic acid residue and by another equivalent (Gln→Glu) substitution within the sequence 114-169. The leucine residue at position 93 was identified in the plasmin-induced peptide (f49-99) by electrospray ionization tandem mass spectrometry (ESI-MS2), and confirmed by the amino acid composition of this peptide C-terminus. This mutation would correspond to the substitution of the codon ATG by CTG, originally reported in cDNA by Jimenez-Flores et al. [11]. The molecular mass of β-casein H was measured as 23 969.1 ± 2.4 ġmol-1.