Hydrolysis of galactdipids by human pancreatic lipolytic enzymes and duodenal contents

Monogalactosyldiacylglycerols (MGDG), digalactosyl- diacylglycerols (DGDG) and sulfquinovmyldiacylglycerols (SQDG) are major lipids in vegetable food. Their digestion and absorp- tion are unknown. This study examines the hydrolysis of galac- tolipids in vitro with human duodenal contents, pancreatic juice, and purified human pancreatic lipases. Galactolipids were incubated with human duodenal contents, pancreatic juice, pure pancreatic carboxyl ester lipase (GEL), and colipase-dependent lipase with colipase (Lip-Col). Hydrolysis was estimated as release of free fatty acids and by the use of (3H)galactose or (3H)fatty acid-labeled DGDG. Pancreatic juice and duodenal contents hydrolyzed DGDG to fatty acids, digalactosylmono- acylglycerol (DGMG) and water-soluble galactose-containing compounds. The hydrolysis of DGDG was bile salt-dependent 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 three substrates; the hydrolysis rate was MGDG > SQDG > DGDG. Pure Lip-Col had activity toward MGDG but had little activity against DGDG. Separation of pancreatic juice by Sephadex GlOO gel filtration chromatogra- phy revealed two peaks with galactolipase activity that coincided with CEL (molecular mass 100 kD) and lipase (molecular mass 50 kD) peaks. In contrast to pure Lip-Col enzymes of the latter peak were as active against DGDG as against MGDG. BP Thus, DGDG is hydrolyzed both by CEL and by a pancreatic en- zyme(s) with a molecular mass of 40-50 kD to fatty acids and lyso DGDG. MGDG, DGDG, and SQDG are all hydrolyzed by human pancreatic juice. Pure CEL hydrolyzed all three sub- strates.-Andersson, L., C. Bratt, K. C. Arnoldsson, B. Herslof, N. U. Olsson, B. Sternby, and A. Nilsson. Hydrolysis of galactolipids by human pancreatic lipolytic enzymes and duo- denal contents. J Lipid Res. 1995. 36: 1392-1400. cellular membranes because about 77% of the lipids are neutral galactosyldiacylglycerols (1). Of the total nonpig-