Formation of lactose in homogenates of mammary gland.

In 1935, Grant (1) successfully demonstrated the in vitro biosynthesis of lactose from glucose in slices of guinea pig mammary gland. Lactose was determined by a differential fermentation method. Under the conditions employed, sugar phosphates were not converted to lactose either in slices or minces of lactating gland. Recently this work was confirmed and extended by Malpress and Morrison (a), who found glucose, glycogen, and maltose’ to give rise to lactose in slices of lactating mammary gland. These workers used a calorimetric method for determining lactose (3). Again, attempts to obtain active extracts met with failure. The various mechanisms proposed to account for the conversion of glucose to lactose have been discussed by Folley (4). It is obvious that two major obstacles bar progress on this problem. First, it is necessary to obtain a homogenate or extract which retains the capacity to synthesize lactose. Secondly, it is necessary to devise a method for determining lactose which is specific, sensitive, and, if possible, suitable for routine work. In the following it will be shown that it is possible to prepare from the lactating mammary gland of the guinea pig a homogenate capable of lactose synthesis. Such preparations have been used to examine a variety of substrates suspected of being lactose precursors.