On the Identity between the Small Intestinal Enzymes Phlorizin Hydrolase and Glycosylceramidase*

Lactase-phlorizin hydrolase complex isolated from the membrane fraction of the small intestine of Z-week-old rats has a glycosylceramidase activity similar to that reported by Brady et al. ((1965) J. BioZ. Chem. 240, 3766). The glycosylceramidase activity corresponds to phlorizin hydrolase rather than to lactase. The “physiological” substrates of small intestinal phlorizin hydrolase (the activity of which is high at birth and declines at the time of weaning) are most probably glucosylceramides and lactosylceramides, both of which are components of the fat globules in milk.