A nitrogenous derivative of lactose from lactating rat mammary gland

During an investigation of the synthesis of lactose by various preparations from rat mammary glands (see Heyworth & Bacon, 1955) a new substance was noticed on paper chromatograms of extracts made in the early stages of lactation. Shortly afterwards Caputto & Trucco (1952) reported the presence in such extracts of several oligosaccharides, one of which they suggested was a tetrasaccharide. We attempted the isolation of the substance, with the possibility in view that it arose as a by-product or intermediate in lactose synthesis. The idea that it was exclusively carbohydrate in nature was weakened by the discovery that acid hydrolysis only doubled its reducing power, and after the report by Leloir & Cardini (1953) that Caputto & Trucco's compound was a nitrogenous derivative of lactose we found that our own partially purified prepara- tions also contained nitrogen. Although our method of purification differs considerably from that used by Our compound, like 'neuramin- lactose' and 'compound E' (Caputto & Trucco, 1952), gives the direct Ehrlich reaction and a purple colour with Bial's reagent, which are characteristic of sialic acid Although we normally used boiling water for its extraction, it may equally well be extracted with cold water. It therefore has a particular interest as a naturally occurring de- rivative of sialic acid of low molecular weight; hitherto sialic acid has been found only in mucins, glycoproteins and complex lipids.