A novel proteinase from human pancreas

Area of Science:

• Biochemistry
• Enzymology
• Human Physiology

Background:

• A previously isolated cholesterol-binding protein from human pancreas (Mr 28,000, pI 4.9) was characterized.
• Proteolytic activity was found to be intrinsically linked to this cholesterol-binding protein.

Purpose of the Study:

• To investigate the nature of the observed proteolytic activity associated with the cholesterol-binding protein.
• To characterize the enzyme's substrate specificity, catalytic mechanism, and interactions with protease inhibitors.

Main Methods:

• Enzyme activity assays using specific substrates (e.g., benzyloxycarbonylalanine p-nitrophenyl ester).
• Inhibition studies with phenylmethanesulphonyl fluoride.
• Autoradiographic analysis of interactions with serum protease inhibitors (alpha 1-antitrypsin, alpha 2-macroglobulin).

Main Results:

• The enzyme activity was inseparable from the cholesterol-binding protein and showed parallel degradation with denaturants.
• The proteinase efficiently cleaved benzyloxycarbonylalanine p-nitrophenyl ester but not substrates for elastase, trypsin, or chymotrypsin.
• It was identified as a serine proteinase, inhibited by phenylmethanesulphonyl fluoride, and bound to alpha 1-antitrypsin and alpha 2-macroglobulin.

Conclusions:

• The isolated protein is a novel serine proteinase from the human pancreas, provisionally named 'cholesterol-binding pancreatic proteinase'.
• This proteinase constitutes a significant component (4-6%) of human pancreatic secretions.