BIOSYNTHESIS AND COMPOSITION OF MILK.

Some of the constituents of milk are unbiquitous biochemical compounds and others are unique products of the mammary gland. Lactose, the distinctive milk disaccharide, caseins, a group of phosphoproteins, and fat are present in nearly all milks that have been examined and the pathways involved in their biosynthesis are discussed in this paper. Milks of various species differ quantitatively in the proportions of their principal constituents. These differences suggest phylogenetic grouping and undoubtedly reflect evolutionary divergence. The extent to which this divergence has been affected by the nutritive requirements of the young, by the dietary sources of the lactating female, and by various other environmental factors has not been completely clarified. Evolutionary divergence is also evident in the composition and amino acid sequences of several families of milk proteins. The relationship between such differences and the function of these proteins has not yet been elucidated. [ABSTRACT FROM AUTHOR]