Nomenclature of Proteins of Cow's Milk: Fifth Revision

Abstract This report reviews changes the nomenclature of bovine milk proteins necessitated by recent advances of our knowledge. Identification of a number of milk proteins ( α s1 -, β -, and κ -caseins; α -lactalbumin and β -lactoglobulin) continues to be based upon their primary structures (amino acid sequences). Since our last report, α s2 -casein and serum albumin can be added to the list of major milk proteins for primary structure is known. Changes recommended in the nomenclature of caseins are primarily a result of differences within this family of proteins brought about by posttranslational modification. For example, α s0 -casein is identical to α s1 -casein, and α s3 -, α s4 -, and α s6 -caseins are identical to α s2 -casein except for differences in degree of phosphorylation. Additionally, proteose-peptone components 5, 8-slow and 8-fast, and γ 1 -, γ 2 -, and γ 3 -caseins are N-terminal and C-terminal fragments, respectively, of β -casein formed during proteolysis by plasmin. Nomenclature of immunoglobulins remains consistent with guidelines for human proteins and is based largely upon crossreactivity with reference proteins. The minor whey protein lactollin is β 2 -microglobulin for which the sequence of amino acids is known. An operational definition for proteins associated with the milk fat globule membrane has been developed. Nomenclature initially suggested for these proteins was based upon their electrophoretic behavior under a given set of conditions. Because of increased interest in milk proteins of species other than bovine, the Committee suggests that these be identified as homologs of those already characterized in European, Bos taurus , and Indian, Bos indicus , cattle. Guidelines are given to aid in determining if homology exists. Provisional nomenclature is suggested for use in the interim until homology can be established.