Characterization of lecithin–cholesterol acyltransferase from human plasma. 3. Chemical properties of the enzyme

Publisher Website
Google Scholar
Abstract
The polypeptide MW of lecithin-cholesterol acyltransferase (LCAT) (45,000) was obtained by deducting the weight of carbohydrate moiety (25%, wt/wt) from the total MW of 60,000. LCAT had a relatively high content of glutamic acid, aspartic acid, glycine and leucine residues, and 4 half-cystines. The carbohydrate content was .apprx. 25% (wt/wt): hexoses, 13%; hexosamines, 6.2% and sialic acid, 5.4%. The total number of 408 amino acid residues/mol and the mean residue weight of 110.3 were found. From fluorescence spectroscopy analysis, 6-7 mol of tryptophan were found per mole of LCAT in 10 mM phosphate (pH 7.4). However, when LCAT was digested by the mixture of chymotrypsin and ponase, the tryptophan residues increased to 10-11 mol/mol of LCAT, which agrees well with data obtained previously by UV absorption spectroscopy. A partial specific volume of 0.707 ml/g was determined by compositional analysis. Human LCAT had a relatively high extinction coefficient .**GRAPHIC**. of 21 at 280 nm and neutral pH. Two residues of cysteine per mole of LCAT were estimated both in the presence or absence of sodium dodecyl sulfate by titration with 5,5''-dithiobis-2-nitrobenzoic acid. The enzyme showed a lower tendency to staining with Coomassie blue R-250 than bovine serum albumin. The enzyme was rapidly inactivated by DFP regardless of whether or not the free SH was blocked. The enzyme was also irreversibly inhibited by cysteine above concentrations of 1 mM. Neither the high density lipoprotein nor liposome substrate was able to protect against the inhibition by cysteine or DFP.

This publication has 1 reference indexed in Scilit: