Bovine alpha s0 casein; a phosphorylated homologue of alpha s1 casein.

After consideration of its electrophoretic behaviour, amino acid composition and phosphate content, bovine alpha s0 casein has been shown to differ from alpha s1 casein only in respect of its phosphate content. The presence in alpha s0 casein of one phosphate residue more than occurs in alpha s1 casein was confirmed by comparative degradative studies performed on both proteins. From these it was concluded that alpha s0 casein may be considered as being alpha s1 casein which has been modified by phosphorylation of the seryl residue located at position 41.