Abstract
Pectins are complex acidic polysaccharides that are major components of plant cell walls. Polygalacturonic acid (PGA) is a major backbone of pectins. PGA synthase, which successively transfer galacturonic acid to produce PGA, is a key enzyme for biosynthesis of pectins. This enzyme has not been purified to homogeneity nor has its gene been cloned. We have constructed the assay method for PGA synthase using pyridylaminated oligogalacturonic acid, leading to the detection of successive glycosyltransfer activity of the enzyme. In this study, we show that PGA synthase exists as a protein complex.
The solubilized enzyme was prepared from the microsome fraction of pea seedling. The activity was inhibited by preincubation in the buffers containing more than 200 mM NaCl or KCl. The solubilized enzyme had a Stokes radius and a sedimentation coefficient comparable to those of ribosome. These data indicate that PGA synthase exists as a protein complex.
