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.
KeywordsCholesterol Sugar Agar Urea Carbohydrate
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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