This rapid screening procedure for detection of low but functional elastase-inhibitory activity in human plasma is based on the fact that incubation of excess porcine pancreatic elastase (EC 3.4.21.36) with plasma results in formation of a complex with active alpha 1-proteinase inhibitor (alpha 1PI, also called alpha 1-antitrypsin). In normal individuals all of the elastase is complexed, leaving no free enzyme to hydrolyze the elastase substrate, and the reaction mixture remains clear. Because individuals homozygous for the Z allele have relatively low concentrations of alpha 1PI, their plasma cannot complex all of the elastase in the assay. The uncomplexed enzyme hydrolyzes the elastase-specific p-nitroanilide substrate, producing a yellow reaction mixture. Use of this simple assay for early screening of individuals for alpha 1PI deficiency may substantially decrease the number of untreated cases of familial emphysema, a disorder that develops as a result of a genetically derived proteinase-proteinase inhibitor imbalance.
11Ptions of cholesterol caused very marked changes in the rate of hydrolysis of soybean oil. At low concentrations of cholesterol (5%) an optimum activity occurred in the presence of 20% phospholipid. With 15% cholesterol the optimum concentration of phospholipid was 30%, and at 30% cholesterol the optimum concentration of phospholipid was 50%. The relative activity at these optimum phospholipid concentrations was 65, 100 and 70% respectively.These results show that the lipid composition of the substrate emulsion has a very marked effect on the activity of lipoprotein lipase. It is also known that surface-active agents used in the preparation of emulsions influence the activity (Fielding, 1970a; Doizaki & Zieve, 1968), but it is not yet known whether changes in plasma-lipid composition affect the tissue uptake of circulating triglyceride. The results of these experiments in vitro would suggest that the cholesterol concentration and the relative composition of the plasma lipids could be of importance in the activity of lipoprotein lipase in vtvo.
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