Characterization of lecithin:Cholesterol acyltransferase from human plasma: II. Physical properties of the enzyme |
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Authors: | Kui-Song Chong Shinichi Hara Richard E Thompson Andras G Lacko |
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Institution: | 1. Department of Chemistry, Division of Biochemistry, North Texas State University, Denton, Texas 76203 USA;2. Department of Biochemistry, Texas College of Osteopathic Medicine, Denton, Texas 76203 USA |
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Abstract: | The physical properties of purified human plasma lecithin:cholesterol acyltransferase (LCAT) were investigated by techniques including analytical ultracentrifugation, ultraviolet spectroscopy, electrofocusing, and circular dichroism. The partial specific volume of LCAT was determined by sedimentation equilibrium ultracentrifugation experiments in H2O and D2O solutions (0.702 ml/g). The Mr was 67,000 by sodium dodecyl sulfate (SDS)-gel electrophoresis and 60,000 by sedimentation equilibrium ultracentrifugation. The discrepancy between the two sets of data presumably arose from the glycoprotein nature of the enzyme. Studies of the ultraviolet spectrum indicated that LCAT contained 6.5% () tyrosine which corresponds to approximately 18 tyrosine residues/mol of LCAT (polypeptide Mr 45,000). Spectrophotometric titration of the ionizable phenolic side chains indicated that nearly all the tyrosine residues were buried at neutral pH while they became gradually exposed at higher pH. The apparent pK of this transition was about 12.0 contrasted with 9.8, the apparent pK of ionization of the free tyrosyl groups. |
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Keywords: | To whom correspondence should be addressed: P O Box 13408 Department of Biochemistry Denton Tex 76203 |
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