Absence of beta-galactosidase (lactase) activity from intestinal brush borders of suckling macropods: implications for mechanism of lactose absorption.

1. Neutral beta-galactosidase (lactase) activity was absent from crude brush borders of small intestines of three species of suckling macropods (kangaroos and wallabies), even though the intestinal mucosal homogenates had high beta-galactosidase activities. 2. These activities were entirely due to an intracellular acid beta-galactosidase, probably located in lysosomes. 3. The results suggest that the absorptive-digestive mechanism for lactose in macropods is fundamentally different from that in eutherian mammals.