The aim of the present study was to purify and clone the trypsinogen isoforms
from the guinea pig pancreas and characterize their activation properties.
Trypsinogens from pancreatic homogenates were isolated by ecotin
-affinity chromatography, followed by cation-exchange chromatography. Activation of trypsinogens was tested with enteropeptidase
, cathepsin B
, and trypsin. Complementary DNAs for pretrypsinogens were cloned from total RNA after reverse transcription and polymerase chain reaction amplification.
Purification of trypsinogens yielded a single peak with an N-terminal amino-acid sequence of LPIDD. Cloning of pretrypsinogen cDNAs revealed 2 distinct but nearly identical isoforms. At the amino acid level, the only difference between the 2 isoforms is an Ala/Ser change at position 15 within the signal peptide. Thus, both cDNA variants give rise to the same mature trypsinogen upon secretion. Guinea pig trypsinogen is readily activated by enteropeptidase
and cathepsin B
but exhibits essentially no autoactivation
, under conditions where human cationic and anionic trypsinogens rapidly autoactivate.
The observations suggest that multiple trypsinogen isoforms
and their ability to autoactivate are not required universally for normal digestive physiology in mammals. Furthermore, the inability of guinea pig trypsinogen to undergo autoactivation
suggests that this species might be more resistant to pancreatitis than humans, where increased autoactivation
of cationic trypsinogen mutants has been linked to hereditary pancreatitis.