Comparison of dipeptidyl peptidase IV prepared from pig liver and kidney

Dipeptidyl peptidase IV (dipeptidylpeptide hydrolase, EC 3.4.14.-) has been purified from the microsomal fraction of pig liver, using an immunoaffinity chromatography, and its properties compared with those of the enzyme purified from pig kidney. The amino acid compositions of both enzymes were similar. The same kinds of carbohydrates were found in both enzymes, but there were differences in the molar concentrations of individual sugars. The liver enzyme had greater concentrations of mannose, fucose and sialic acid than the kidney enzyme, while the concentrations of galactose and glucosamine were greater in the kidney enzyme. The carbohydrates accounted for approx. 18.3 and 22.7% of the weight of the kidney and liver enzymes, respectively. The pH optima, molecular weights, substrate specificities and Km values of the two enzymes and the effects of diisopropylfluorophosphate on their activities were nearly identical. The liver enzyme was heat- and pH-sensitive, but not attacked by proteinases.