In Vitro Localization of Hydroxyproline O-Glycosyl Transferases in Chlamydomonas reinhardii

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The intracellular location of the two major O-glycosylating enzymes (hydroxyproline-arabinosyl and -galactosyl transferases) involved in the synthesis of the cell wall glycoproteins of Chlamydomonas reinhardii was determined by isopycnic sucrose density gradient centrifugation. A comparison of gradients prepared under low and high Mg^<2+>-conditions has enabled us to clearly allocate the galactosyl transferase to membranes of the Golgi apparatus. In contrast, the membranes which bear the arabinosyl transferase respond to a change in Mg^<2+>-concentration in just the same way as the endoplasmic reticulum does. Analysis of the product formed in vitro from UDP-[^<14>C]arabinose and microsomal membranes has confirmed the synthesis of an arabinose-containing hydroxyproline-rich glycoprotein. Our results indicate that whilst the Golgi apparatus is responsible for some of the glycosylation reactions in hydroxyproline-rich glycoprotein biosynthesis an appreciable portion of the arabinosylation is accomplished while the polypeptide is still in the lumen of the endoplasmic reticulum.
日本植物生理学会の論文