Journal of Lipid Research, Vol. 13, 769-776, November 1972
Copyright © 1972 by Lipid Research, Inc.

Hydrolysis of glyceryl tri[1-¹⁴C]octanoate and glyceryl tri[1-¹⁴C]oleate monolayers by postheparin lipolytic activity

Louis C. Smith

Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77025

The hydrolysis of monomolecular films of glyceryl tri[1-¹⁴C]octanoate and glyceryl tri[1-¹⁴C]oleate has been demonstrated by measurement of the decrease in surface radio-activity that occurs in the presence of postheparin plasma. The hydrolysis displayed first order kinetics and was proportional to enzyme concentration over a 10-fold range. No hydrolysis was observed in the absence of enzyme, and only slight activity (1%) was found in plasma taken from subjects before heparin administration. The hydrolysis was stimulated to a variable extent by Ca²⁺. The first product of hydrolysis of the monolayer was identified as 1,2-diglyceride, which was subsequently converted to 2-monoglyceride. Inhibition of triglyceride hydrolysis was observed when postheparin plasma was preincubated in 2 m NaCl, 10^-4 m protamine, 10 mm Na₄P₂O₇, and 0.1 m NaF. Monolayer techniques avoid some but not all of the problems associated with emulsified lipid substrates and appear to be applicable for study of post-heparin lipolytic activities.

Supplementary key words lipid monolayers • triglyceride • hydrolysis • lipoproteins • lipase

Submitted on March 28, 1972
Accepted on July 24, 1972

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