Lactose or milk oligosaccharide: which is significant among mammals?

Implications ・ α-Lactalbumin, a milk protein, had evolved from c-type lysozyme, and it can associate with β4-galactosyltransferase 1 within the mammary epithelial cells. The acceptor specificity of this enzyme had changed by result of the association of two proteins to biosynthesize lactose. ・ Milk oligosaccharides are biosynthesized in addition to lactose, as lactose is the preferred acceptor for several glycosyltransferases present within the cells. ・ Milk oligosaccharides can be utilized as significant energy sources for the suckling neonates of monotremes and marsupials even though the small intestinal mucosa of these neonates lacks a lactase. ・ Lactose has become a predominant saccharide in the milk of most eutherians, resulting from a hypothetical increase in the expression level of α-lactalbumin. It has become to be utilized as a significant energy source for the suckling neonates, as a result of the acquisition of lactase in the microvilli of small intestinal cells. ・ Human milk contains the oligosaccharides at significant concentrations along with lactose among eutherians, which should be advantageous for symbiosis with beneficial colonic bifidobacteria.