The Activity of Three Different Small-Intestinal β-Galactosidases in Adults with and without Lactase Deficiency

A residual activity of brush border lactase, about 10 per cent of ‘normal’ level, has been demonstrated in adults with specific lactase deficiency. The properties of the residual enzyme were similar to those of the ‘normal’ brush border lactase, indicating that there is a low activity of structurally normal enzyme. The activities of two other intracellular β-galactosidases, acid β-galactosidase and hetero β-galactosidase, were the same in lactase-deficient individuals and in controls. The acid β-galactosidase also has lactase activity in vitro and is responsible for about 1 U/g protein of the total lactase activity at pH 6 in mucosal biopsies. The relation of these enzymes to the β-glucosidase activity was also studied.