Starch synthesis in wood of Juglans regia: Role of ADP-glucose pyrophosphorylase

ADP-glucose pyrophosphorylase from walnut wood (J. regia L.) was purified 50 fold to a specific activity of 2.6 mu moles glucose-1-P produced per minute per milligram protein. Wood from young plants was ground in liquid N-2 after accurate removal of all the cortical parenchyma. The specific activity in the starting material was very low and the enzyme was quite unstable. Precipitation with 18% PEG was carried out to concentrate and stabilise the activity. Further purification was attained with DEAE Sepharose and MonoQ ion exchange chromatography. In both cases the activity was eluted with linear NaCl gradients. The partially purified enzyme was very sensitive to allosteric activation and inhibition by 3-phosphoglycerate (3PGA) and Pi respectively, even if assessed in the pyrophosphorolytic direction. ADP-glucose pyrophosphorylase from walnut wood, as those from many other higher plant tissues, may be strongly regulated by allosteric control, this could be one of the control sites of in vivo starch deposition in wood.