Enzymes of Galactose Synthesis in Mammary Gland and Mammary Tumors of the Rat.

As part of studies now under way in our laboratory devoted to determining the degree of loss or retention of functional enzymatic activities in the transformation of normal to neoplastic cells, it was deemed desirable to study, both in the normal mammary gland and in mammary tumors, the levels of certain enzymes specifically involved in the production of lactose. This substance is formed, perhaps exclusively in the mammary gland, as a milk component. Since the pathway of its formation requires the sequential participation of two enzymes outside of the main routes of glucose metabolism, it was felt that these enzymes would represent a sound parameter for this study. The enzymes are glucose I-phosphate-uridine triphosphate uridylyltransferase (uridine diphosphate glucose pyrophosphorylase) and uridine diphosphate glucose-uridine diphosphate galactose 4-epimerase. A particular additional advantage in the choice of these enzymes is that they are stable, and both can be readily assayed spectrophotometrically. As a preliminary to this comparative study, it was necessary to examine the normal mammary glands of rats for the activity of these enzymes under various physiological conditions. The present report deals with the ranges of these activities displayed by inactive mammary glands of rats, by glands during pregnancy and lactation, and by several types of primary mammary tumors.