Studies on the nature of microsome-bound substances involved in the biosynthesis of acidic glycoproteins of guinea-pig serum

Abstract

1. In further studies on the biosynthesis of components of fraction I, an acidic glycoprotein-containing fraction from guinea-pig serum, an investigation was made of the substances bound to liver microsomes that had earlier been implicated to participate in the synthesis of components of fraction I present in serum. These substances were normally liberated by ultrasonic vibrations. Antisera to subfractions of fraction I were used for characterization. 2. At pH8.6, most of the microsome-bound substances showed electrophoretic mobilities lower than components of fraction I but similar to components of sialic acid-free fraction I. 3. The sialic acid/protein ratios of immune precipitates formed by microsome extracts were similar to those of precipitates formed by sialic acid-free fraction I. 4. On chromatography on Sephadex G-150, most of the microsomal substances were eluted at an essentially similar volume to the main components of fraction I. 5. It was concluded that most of the microsome-bound substances lack sialic acid residues, and, as appreciable degradation of completed molecules is unlikely, these substances appear to be precursors of serum glycoprotein molecules with incomplete prosthetic groups. 6. Evidence was obtained on the submicrosomal localization of incomplete and complete serum glycoprotein molecules.

Studies on Acute Phase Proteins of Rat Serum. III. Site of Synthesis of Albumin and α1-Acid Glycoprotein and the Contents of These Proteins in Liver Microsome Fractions from Rats Suffering from Induced Inflammation

“…precipitin lines formed by extracts of microsome material gave reactions of immunological identity with precipitin lines formed by serum on reaction with antiserum to albumin or al-acid glycoprotein, it does not follow that material present in microsome extracts that is capable of reaction with antiserum to al-acid glycoprotein or albumin represents completed molecules identical with those present in serum. Clycoproteins similar to the al-acid glycoprotein under study in the present work have been shown to be present in microsome material in the form of precursor molecules devoid of some carbohydrate residues (23). Therefore, in the case of al-acid glycoprotein, it is likely that material present in extracts of the microsome fraction that is capable of reaction with antiserum to alacid glycoprotein represents a spectrum of molecules with varying amounts of carbohydrate attached to precursor polypeptide chains.…”

Synthesis and Transport of Hydroxyproline-rich Components in Suspension Cultures of Sycamore-Maple Cells

“…Thus, the nucleotidemediated sugar incorporation observed by Villemez et al might at least in part be the glycosylation of a hydroxyproline-containing component(s). In this connection, it is of interest that glycosylationof variousanimal proteins is mediated not by Golgi bodies but by other smooth surfaced membranes (3,21).…”