Comparative aspects of milk caseins

The caseins comprise the major protein component of milk of most mammals an d are secreted as micelles that also carry high concentrations of calcium. They are phosphoproteins that represent the products of four genes, equival ent to those that encode the bovine alpha(s1), alpha(s2), beta, and kappa-c aseins. There is considerable variation in the relative proportions of the particular caseins across species. The primary sequences of the alpha(s1), alpha(s2), and beta-caseins also show considerable species variation consis tent with rapidly evolving genes that are proposed to have a common precurs or. In contrast, the kappa-caseins exhibit features that demonstrate a sepa rate origin and function where they are proposed to stabilise the micelle s tructure. This review focuses on comparative aspects of the caseins across a number of species for which information is now available. (C) 1999 Elsevi er Science Inc. All rights reserved.