HYDROLYSIS OF GALACTOLIPIDS BY HUMAN PANCREATIC LIPOLYTIC ENZYMES ANDDUODENAL CONTENTS

Monogalactosyldiacylglycerols (MGDG), digalactosyldiacylglycerols (DGD G) and sulfoquinovosyldiacylglycerols (SQDG) are major lipids in veget able food. Their digestion and absorption are unknown. This study exam ines the hydrolysis of galactolipids in vitro with human duodenal cont ents, pancreatic juice, and purified human pancreatic lipases. Galacto lipids were incubated with human duodenal contents, pancreatic juice, pure pancreatic carboxyl ester lipase (GEL), and colipase-dependent li pase with colipase (Lip-Col). Hydrolysis was estimated as release of f ree fatty acids and by the use of [H-3]galactose or [H-3]fatty acid-la beled DGDG. Pancreatic juice and duodenal contents hydrolyzed DGDG to fatty acids, digalactosylmonoacylglycerol (DGMG) and water-soluble gal actose-containing compounds. The hydrolysis of DGDG was bile salt-depe ndent and had a pH optimum at 6.5-7.5. Human pancreatic juice released fatty acids from MGDG, DGDG, and SQDG. Purified CEL hydrolyzed all th ree substrates; the hydrolysis rate was MGDG>SQDG>DGDG. Pure Lip-Col h ad activity toward MGDG but had little activity against DGDG. Separati on of pancreatic juice by Sephadex G100 gel filtration chromatography revealed two peaks with galactolipase activity that coincided with CEL (molecular mass 100 kD) and lipase (molecular mass 50 kD) peaks. In c ontrast to pure Lip-Col enzymes of the latter peak were as active agai nst DGDG as against MGDG. Thus, DGDG is hydrolyzed both by CEL and by a pancreatic enzyme(s) with a molecular mass of 40-50 kD to fatty acid s and lyse DGDG. MGDG, DGDG, and SQDG are all hydrolyzed by human panc reatic juice. Pure CEL hydrolyzed all three substrates.