Abstract
Enzyme activity hydrolyzing an elastase substrate, succinyl-L-alanyl-L-alanyl-L-alanine-p-nitroanilide, was found in serum and bile of patients with obstructive jaundice. Though the enzyme was not elastolytic and was of high molecular weight, it was definitely differentiated from elastase-α2macroglobulin complex because its activity was unaffected by phenylmethylsulfonylfluoride or diisopropylfluorophosphate which inhibited the complex completely.
The high molecular weight enzyme in bile was, as well as glutamyltranspeptidase (GGTP) and leucine aminopeptidase (LAP), changed into smaller forms by means solubilizing membrane such as detergent treatment and trypsin digestion. However, it was, in contrast to GGTP and LAP, almost unchanged by limited papain digestion. The molecular weight of the enzyme molecules obtained by trypsin digestion were 102,000 daltons for the enzyme, 91,000 daltons for GGTP and 174,000 daltons for LAP, respectively. Inhibition study using some chemicals revealed that the enzyme was metal dependent and had disulfide bridges in its structure. The serum enzyme was also changed into the smaller form by the detergent treatment, and shared the same characteristics with the bile enzyme.
These results suggest that the enzyme is associated with liver plasma membrane probably more profoundly buried in the lipid bilayer than GGTP and LAP and that it is one of so-called “biliary tract enzymes” not only because of elevation of serum level in bile flow obstruction but because of the association of liver plasma membrane.
