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 -casein was isolated from individual milk and characterized. It is proposed for nomenclature as -CN H. The variant H differed from the variant A 2 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-MS 2 ), 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 . The molecular mass of -casein H was measured as 23 969.1 2.4 g . mol -1 .