In vivo measurements of control coefficients for hexokinase and glucose-6-phosphate dehydrogenase in Xenopus laevis oocytes

Hexokinase and glucose-6-phosphate dehydrogenase activities were increased in Xenopus laevis oocytes by microinjection of commercial pure enzymes, The effect of increased fractional activities on glycogen synthesis or on the production of (CO2)-C-14 (the oxidative portion of the pentose phosphate pa thway) was investigated by microinjection of [1-C-14]glucose and measuremen ts of the radioactivity in glycogen and CO2. Control coefficients calculate d from the data show that hexokinase plays an important role in the control of glycogen synthesis (control coefficient = 0.7) but its influence on the control of the pentose phosphate pathway is almost nil (control coefficien t=-0.01). Glucose-6-phosphate dehydrogenase injections did not affect the p roduction of (CO2)-C-14 by the pentose phosphate pathway, indicating that o ther factors control the operation of this pathway. In addition, an almost null control of this enzyme on glycogen synthesis flux was observed. (C) 20 00 Federation of European Biochemical Societies. Published by Elsevier Scie nce B.V. All rights reserved.