Abstract
Abstract The stereochemical course of hydrolysis of radioactive triolein was determined using lipoprotein lipase of cow's milk and rat postheparin plasma. [3H]Glycerol trioleate or glycerol [1-14C]trioleate was emulsified with total egg yolk lipids to provide 0.2 to 2.5 µCi of 3H or 0.03 µCi of 14C per µm substrate. The hydrolysis products were isolated at 1 to 45 min and free fatty acids and the various positional isomers of mono- and diglycerides were resolved by thin layer chromatography. In a total yield of 0.03 to 0.16 µmole of diglyceride, 9 to 30% was 1,3- and 70 to 91%, 1,2-(2,3-)diglyceride. The 2,3-isomer was 73 to 96% of the latter. The yield of free fatty acids and monoglycerides varied with the length of incubation. In 15 of 17 determinations, the 1-(3-)isomer accounted for 51 to 87% of the monoglyceride. It is suggested that lipoprotein lipase attacks preferentially position 1 in sn-glycerides and follows it by hydrolysis of the positions 2 and 3. An intermediate formation of 2,3-diglycerides during lipoprotein lipase hydrolysis may be important in avoiding stimulation of triglyceride and phospholipid biosynthesis which proceed via 1,2-diglycerides.
Highlights
The stereochemical course of hydrolysis of radioactive triolein was determined using lipoprotein lipase of cow’s milk and rat postheparin plasma. [3H]Glycerol trioleate or glycerol [lJ4C]trioleate was emulsified with total egg yolk lipids to provide 0.2 to 2.5 PCi of 3H or 0.03 PCi of 14C per PM substrate
The hydrolysis products were isolated at 1 to 45 min and free fatty acids and the various positional isomers of mono- and diglycerides were resolved by thin layer chromatography
This is comparable to the activity reported for milk lipoprotein lipase by Bier and Have1 (8) and Korn (4)
Summary
The stereochemical course of hydrolysis of radioactive triolein was determined using lipoprotein lipase of cow’s milk and rat postheparin plasma. [3H]Glycerol trioleate or glycerol [lJ4C]trioleate was emulsified with total egg yolk lipids to provide 0.2 to 2.5 PCi of 3H or 0.03 PCi of 14C per PM substrate. The stereochemical course of hydrolysis of radioactive triolein was determined using lipoprotein lipase of cow’s milk and rat postheparin plasma. The hydrolysis products were isolated at 1 to 45 min and free fatty acids and the various positional isomers of mono- and diglycerides were resolved by thin layer chromatography. The preferential hydrolysis of the secondary ester bond demonstrated by Greten et al (2) involved a relation of the rate of release of the acids of the second and third positions of the glyceride molecule only. It is shown that purified preparations of lipoprotein lipase from both cow’s milk and rat postheparin plasma release the fatty acids more rapidly from position 1 than from either position 2 or position 3 of the triglyceride molecule. The potential metabolic significance of this observation is briefly discussed
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