Chemical synthesis and biochemical properties of peptide fragments of apolipoprotein-alanine.
Apolipoprotein-alanine is an apolipoprotein isolated from very-low-density lipoproteins of human plasma. This protein contains 79 amino acids and binds phosphatidyl choline. Four fragments of this molecule corresponding to sequence positions 41-79 (I), 48-79 (II), 55-79 (III), and 61-79 (IV) have been synthesized by standard solid-phase methods. The resulting peptides were cleaved from the resin and deblocked with liquid HF, then purified by chromatography on Sephadex G-50 and DEAE-cellulose. Each purified peptide eluted as a single, symmetrical peak, exhibited a single band on polyacrylamide gel electrophoresis, and gave an amino-acid analysis in good agreement with the theoretical value. Circular dichroism studies indicated that only fragments I and II became more helical in the presence of phosphatidyl choline and significantly inhibited the reactivation of delipidated beta-hydroxybutyrate dehydrogenase (EC 1.1.1.30), an enzyme that requires phosphatidyl choline for activity. When subjected to ultracentrifugation at density 1.064 g/ml in the presence of phosphatidyl choline, fragments I, II, III, and IV floated to the top of the tube to the extent of 85, 50, 13, and 9%, respectively. These results indicate that residues 55-79 do not contain the minimum determinants required for the binding of phospholipid. However, extension of the peptide's N-terminus by seven residues produces a molecule that does bind phosphatidyl choline.
D000409:Alanine; D000595:Amino Acid Sequence; D001059:Apoproteins / Q000138:chemical synthesis; D002499:Centrifugation, Density Gradient; D002848:Chromatography, DEAE-Cellulose; D002850:Chromatography, Gel; D002942:Circular Dichroism; D004591:Electrophoresis, Polyacrylamide Gel; D006884:Hydroxybutyrate Dehydrogenase / Q000037:antagonists & inhibitors; D007118:Immunoassay; D005779:Immunodiffusion; D050356:Lipid Metabolism; D008074:Lipoproteins / Q000138:chemical synthesis*; D008079:Lipoproteins, VLDL / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology; D010713:Phosphatidylcholines / Q000378:metabolism
D001059:Apoproteins; D008074:Lipoproteins; D008079:Lipoproteins, VLDL; D010713:Phosphatidylcholines; D006884:Hydroxybutyrate Dehydrogenase; D000409:Alanine