Evidence for several galactan synthases in flax (Linum usitatissimum L.) suspension-cultured cells

A membrane fraction from flax cells was able to incorporate [(14)C]galactose from UDP-D- [(14)C]galactose in vitro. The products of the reaction, characterized by methylation analysis, consisted of a beta-1,4-galactan (solubilized mainly in water) and a beta-1,3-, beta-1,6-galactan (solubilized mainly in alkali). These results indicated the presence of several galactan synthase complexes, as did a profile of the relationship between pH and activity which revealed both a maximum at pH 6.5 and a shoulder at pH 8. Moreover, galactan synthase activities were found at two densities: 1.125 g cm(-3) (Golgi membranes) and 1.07-1.08 g cm(-3) (corresponding to low-density vesicles). Partial characterization of one enzymatic system (maximally active at pH 8 in the presence of 5 millimole MgCl2) was achieved. The Km for UDP-galactose and Vmax were 38 micromolar and 4.5 nmol h(-1) (mg protein)(-1), respectively.