Properties of pteroylpolyglutamate hydrolase in pancreatic juice of the pig

Abstract

The function of pteroylpolyglutamate hydrolase (PPH) of pancreatic secretion in the hydrolysis of dietary polyglutamyl folates (PteGlun) in humans is unclear. In this study, PPH was detected in pancreatic juice collected from pigs during both fasting and postprandial conditions. The secretion of PPH was markedly increased following feeding. Pancreatic PPH showed the following characteristics: 1) endo/random hydrolysis of gamma-glutamyl peptide bonds of Pte-Glun substrates, yielding folic acid as the terminal product; 2) maximum activity at pH 4.0-4.5 and maximum stability at pH 7.0; 3) stimulation of activity by Zn2+ and 2-mercaptoethanol; 4) Km values for pteroyltriglutamate (PteGlu3) of 28.7 microM at pH 4.0 and 9.1 microM at pH 5.0; 5) apparent molecular weight of 29,000; and 6) isoelectric point within the range of 8.5-9.0. On the basis of PPH activity, volume of the postprandial secretion and pH profile of enzyme activity, it is suggested that pancreatic PPH may act in vivo in folate digestion and absorption to initiate the deconjugation of dietary PteGlun prior to the action of jejunal brush border PPH.