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 dioleoyl2 [l W]oleoyl sn glycerol; rnc-1,2-octadecenyl-3-[9,103H]oleoyl sn glycerol; 2,3 octadecenyl 1 [9,10 3H]oleoylsn glycerol ; and 1,3 -octadecenyl-2 -[9,10 3H]oleoyl-snglycerol. 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.