Isolation and characterization of the proximal and distal forms of lactase-phlorizin hydrolase from the small intestine of the suckling rat.

The complex between lactase (beta-D-galactoside galactohydrolase, EC 3.2.1.23) and phlorizin hydrolase (glycosyl-N-acylsphingosine glycohydrolase, EC 3.2.1.62) has been purified from the proximal and distal regions of the small intestine of suckling rats. The two enzymes behaved differently on DEAE-cellulose ion-exchange chromatography and during electrophoresis in the presence and absence of sodium dodecyl sulphate (SDS), but they have very similar cyanoge bromide cleavage patterns. Kinetic studies on the proximal and distal enzymes showed the same pH optimum of 6.0 and the same heat stability at 45 degrees C, but a small difference in Km. Treatment of both enzymes with fucosidase, mannosidase or N-acetylhexosaminidase did not affect enzymic activity or electrophoretic mobility. Neuraminidase digestion abolished the electrophoretic differences and gave two active enzymes with similar isoelectric points.