Positional Specificity of Triglyceride Lipases in Post-Heparin Plasma

The stereochemistry of the hydrolysis of radioactive glyceryl trioleate and glyceryl diether-monoesters by lipase activity in post-heparin plasma from man, normal and hepatectomized rats, and rat liver perfusate was determined. The following substrates were chemically synthesized and employed in albumin-Triton X-100 emulsions: 1,2-dioleoyl-3-[9,10-3H]oleoyl-sn-glycerol; 1,3-dioleoyl-2-[1-14C]oleoyl-sn-glycerol; rac-1,2-octadecenyl-3-[9,10-3H]oleoyl-sn-glycerol; 2,3-octadecenyl-1-[9,10-3H]oleoyl-sn-glycerol; and 1,3-octadecenyl-2-[9,10-3H]oleoyl-sn-glycerol. The yields of free fatty acid and glycerol varied with different enzyme sources. Km values were determined. Lipases in post-heparin plasma of hepatic and extrahepatic origins attack preferentially positions 1 and 3 in sn-glycerides and do not appear to distinguish between them. The presence in plasma of monoglyceride hydrolase activity that is primarily derived from the liver was confirmed.