CHANGES IN ACTIVITY OF DGLUCOSE-6-PHOSPHATE: NADP AND 6-PHOSPHO-D-GLUCONATE: NADP OXIDOREDUCTASES IN RELATION TO LIGNIFICATION OF BAMBOO

Abstract

D-Glucose-6-phosphate: NADP oxidoreductase (glucose-6-phosphate dehydrogenase; EC 1.1.1.49) and 6-phospho-D-gluconate: NADP oxidoreductase (6-phosphogluconate dehydrogenase; EC 1.1.1.44) were found to be present in immature bamboo. Optimal pHs of the glucose-6-phosphate- and 6-phosphogluconate dehydrogenases were found to be 8.0 and 8.5, respectively. Both enzymes were demonstrated to be NADP-specific and NADP could not be replaced by NAD. Fructose-6-phosphate was indirectly utilized after convrsion to glucose-6-phosphate by glucose-6-phosphate isomerase coexisting in the enzyme preparation. Pattern of enzyme activity and of respiratory breakdown of glucose-1-¹⁴C and glucose-6-¹⁴C were investigated in connection with lignification of bamboo and discussed in comparison with sugar metabolism of fungi-infected plant tissues. As for the changes in the enzyme activity with growth of bamboo, it was recognized that there was a tendency that the activity of both enzymes increased and was maintained at a certain level even in the aged tissues. In addition there was a drop of the C₆/C₁ ratio toward the tissues of lower parts containing considerable amount of lignin and this phenomenon was the same as that observed in pentose phosphate metabolism of fungi-infected plant tissues.