Lactose synthesis in the mammary gland perfused with 1-C14-glucose.

The problem of lactose synthesis in the mammary gland is two-fold: (a) the mechanism by which galactose is formed and (b) the mechanism of condensation of t’he monosaccharide precursors to form the disaccharide. Several mechanisms for the glucose-galactose interconversion in nature have been postulated: (a) Walden inversion of the hydroxyl on carbon atom 4 of glucose (Rohman (I), Robinson (a), Caputto et al. (3)); (b) condensation of two trioses catalyzed by an aldolase reaction (4) (the presence of aldolase in milk was reported by Polis and Shmukler (5)) ; (c) cyclit.ols such as L-inositol (Fischer (6)) or muco-inositol (Topper and Stetten (7)) may be intermediates in the conversion. The work reported here was undertaken with the object of throwing some light on the mechanism of lactose format.ion by studying radioactivity distribution in lactose of milk from a mammary gland perfused with l-C?*glucose. It was found that the lactose synthesized contained about equal amounts of radioactivity in the glucose and galactose moieties. Virtually all of the isotope in each of the monosaccharides was in carbon atom 1.