Extraction and characterization of the enzymes of fructan biosynthesis in timothy (Phleum pratense)

摘要

A preparation of phlein sucrase from seedling shoots of timothy (Phleum pratenseL.) is described which catalyzed the synthesis of fructan with a mean molecular size of 34ensp;000 using sucrose as the substrate. Activity was fully sedimentable at 25ensp;000ensp;times;ensp;g, had a pH optimum of 7.0, and aKmfor sucrose of 0.15ensp;M. Activity was inhibited by beta;-mercaptoethanol and sodium diethyl dithiocarbamate. Raffinose and stachyose, but not members of the kestose series of oligofructans, could act as fructosyl donors in addition to sucrose. Formation of oligosaccharides during high molecular weight fructan synthesis was minimal, with synthesis occurring by a mechanism apparently analogous to bacterial levansucrase. These observations are discussed in relation to thein vivopatterns of fructan biosynthesis observed in different species of higher plants.