A new bovine $\beta$-casein genetic variant characterized by a Met$_{93} \rightarrow$ Leu$_{93}$ substitution in the sequence A$^2$

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 A 2 by the substitu- tion 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) substitu- tion within the sequence 114-169. The leucine residue at position 93 was identified in the plasmin-in- duced peptide (f49-99) by electrospray ionization tandem mass spectrometry (ESI-MS 2 ), and confirmed by the amino acid composition of this peptide C-terminus. This mutation would corre- spond 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 g.mol -1 .