Determination of lipoprotein-lipase activity in human skeletal muscle tissue.
An in vitro assay system was developed for the determination of lipoprotein-lipase activity in 10--30-mg specimens of human skeletal muscle tissue. The reaction medium of the assay was based on a glycine buffer of pH 8.3 (at 37 degrees C) with a heparin concentration of 1.5 g/l (about 180 IU/ml). The enzyme activity was measured as the release of [3H]oleic acid from a serum-activated, triglyceride emulsion, in which [3H]trioleate was used as trace substance. The enzyme activity studied had the characteristic properties of lipoprotein-lipase activity, i.e. it was activated by the addition of serum or apolipoprotein C-II and inhibited in the presence of high ionic strength, protamine sulphate or apolipoprotein C-III. A mean Km of 0.40 +/- 0.13 (S.D.) mmol/l for triglyceride substrate was found in tissue samples that had very different concentrations of lipoprotein-lipase activity. This Km was similar to the low fasting concentrations of very low density lipoprotein triglycerides often found in healthy individuals. The lipoprotein-lipase activity was not decreased freezing and storing the tissue specimens in liquid nitrogen. The within-day variation of the method was 16 percent and the between-day variation 8 percent. Muscle tissue from the vastus lateralis muscle had, on the average, a 60 percent higher concentration of lipoprotein-lipase activity than the rectus abdominis muscle in the same subject.
D000273:Adipose Tissue / Q000201:enzymology; D001053:Apolipoproteins / Q000494:pharmacology; D005615:Freezing; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008071:Lipoprotein Lipase / Q000378:metabolism*; D008722:Methods; D009132:Muscles / Q000201:enzymology*; D009994:Osmolar Concentration; D011479:Protamines / Q000494:pharmacology; D014280:Triglycerides / Q000494:pharmacology
D001053:Apolipoproteins; D011479:Protamines; D014280:Triglycerides; D006493:Heparin; D008071:Lipoprotein Lipase