A comparison of the active site of maltase-glucoamylase from the brush border of rabbit small intestine and kidney by chemical modification studies.

The neutral maltase-glucoamylase complex has been purified to homogeneity from the brush-border membrane of rabbit intestine and kidney. Chemical modification of the amino acid side chains was carried out on the purified enzymes. Studies on the kidney enzyme revealed that tryptophan, histidine and cysteine were essential for both maltase and glucoamylase activities, whereas tryptophan, histidine and lysine were essential for the maltase and glucoamylase activities of the intestinal enzyme. Though there was no difference in the amino acids essential for the hydrolysis of maltose and starch by any one enzyme, starch hydrolysis seems to require two histidine residues instead of the one which is required for maltose hydrolysis. This appears to be true for both the intestinal and kidney enzymes.