Isoforms of procarboxypeptidase B, (pancreas-specific protein, PASP) in human serum, pancreatic tissue and juice

Abstract

Human Pancreas-Specific Protein (PASP) has been described as a useful serum marker for pancreatic graft rejection and acute pancreatitis. By molecular cloning PASP has recently been identified as procarboxypeptidase B (PCPB).

By use of SDS-gel electrophoresis and Western blots, PASP isoforms (proteins interacting with PASP-antiserum) have now been explored in serum and pancreatic tissue and juice.

In serum from healthy volunteers, six different isoforms could be visualised. Their MW varied as follows: > 100 K, about 100 K, 45 K, 35-40 K (two bands) about 30 K and 16 K. The 45 K band, corresponding to PASP purified from pancreatic tissue, was always the major band. In pancreatic cytosol and pancreatic juice, the major band corresponded to PASP (45 K) but weak bands were also seen at MW of 40, 30 and 16 K.

In serum from 15 patients with acute pancreatitis, PASP was highly increased. Bands corresponding to PASP/PCPB as well as carboxypeptidase B (CPB) were seen simultaneously. During recovery PASP in serum was normalised and the CPB band disappeared.

During 12 episodes of pancreatic graft rejection, PASP in serum was also increased but no changes of isoforms in serum were detected. However during these episodes isoforms in pancreatic juice changed dramatically. The band corresponding to PASP disappeared or became much weaker and only bands with lower MW were seen.

We have thus observed changes in PASP/PCB serum isoforms during episodes of acute pancreatitis but not at graft rejection episodes although the total increase of PASP in serum was of the same magnitude.

This convergence of PASP to proteolytic cleavage products may be utilised to differentiate between graft rejection episodes and acute pancreatitis.

Key Words:

• Carboxypeptidases
• isoforms
• pancreatic transplantation
• pancreatitis
• rejection
• Western blot