UDP-glucose Pyrophosphorylase from Tubers of Jerusalem Artichoke (Helianthus tuberosusL.)

UDP-glucose pyrophosphorylase of Jerusalem artichoke tubers was purified 90-fold over the crude extract. The purified enzyme preparation absolutely required magnesium ions for activity. Cobalt ions were 60% as effective as magnesium ions; other divalent cations including manganese showed little or no effect. This enzyme had a pH optimum of 8.5 and a temperature optimum of 40°C. ATP and UDP inhibited the activity of this enzyme in both forward and backward directions. Km values for UDP-glucose, inorganic pyrophosphate, glucose-1-phosphate and UTP were determined to be 4.45 × 10‒4 M, 2.33 × 10‒4 M, 9.38 × 10‒4 M and 2.98 × 10‒4 M, respectively. These results are discussed in comparison with those of UDP-glucose pyrophosphorylases isolated from other plants.