Apoprotein S Versus SAA Protein
Intravenous glucose infusions into neurological patients and post-surgery patients increased dramatically the amount of new polypeptides associated with high density lipoproteins, reaching up to 40% of total apoproteins whereas plasmas of normal subjects fed a regular diet contained only traces of these peptides (0.1%). This increase was observed in HDL2 as well as in HDL3 and also in very low density lipoproteins. Eight polymorphic forms of these new apoproteins named S (sugar induced) were isolated and defined by successive gel chromatography, ion-exchange chromatography, polyacrylamide gel electrophoresis and isoelectric focusing. Apoprotein S did not react with antisera prepared to apo B, apo C, apo A-I and apo A-II, but S4 and S5 gave a positive reaction with anti SAA.
Polypeptides S4 and S5 were recognized to have a high affinity for artificial lipid complexes. The change in the microviscosity of the apoprotein S-dimyristosyl-phosphatidylcholine and apo S-DMPC-cholesterol complexes with temperature, was similar to that observed for apo A-II and a stable complex might be isolated by sepharose 4B chromatography.
The simultaneous appearance of radioactivity into apoproteins S and other apoproteins of HDL (A-I, A-II and C) after the intravenous injection of l-14 C-leucine suggests a common hepatic origin.
Aminoacid composition and partial sequence of apoprotein S were almost identical to those of SAA protein. Similarities and differences between apoprotein S and SAA protein are discussed. The putative precursor role played by apoprotein S in the formation of amyloid may build a link between glucose supply in the diet and tissue deposits observed in atherosclerosis.
KeywordsHigh Density Lipoprotein Glucose Infusion Partial Amino Acid Sequence Lipid Research Clinic Program Human High Density
Abbreviations and Nomenclature
very low density lipoproteins (d < 1.006 g/ml)
high density lipoproteins (d=l.063-1.210 g/ml)
- HDL2 and HDL3
respectively d=l.063-1.125 and 1.125-1.210 g/ml
- Apoprotein Sx
replaces SV-Dx and means Subfraction x of DEAE cellulose chromatography of Fraction V obtained from Sephacryl S-200 chromatography of HDL apoproteins
polyacrylamide gel electrophoresis
serum amyloid A protein
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