PARTIAL-PURIFICATION FROM POTATO-TUBERS OF 3 FRUCTOKINASES AND 3 HEXOKINASES WHICH SHOW DIFFERING ORGAN AND DEVELOPMENTAL SPECIFICITY

A combination of chromatography on DE-52 cellulose, Cibacron Blue agar ose, Mono Q anion exchanger and gel filtration was used to resolve dif ferent hexose-phosphorylating enzymes from growing ''sink'' potato tub ers (Solanum tuberosum L.). Three enzymes (fructokinases: FK1, FK2 and FK3) are active with fructose and inactive with glucose, and three (h exokinases: HK1, HK2 and HK3) are active with glucose but not with fru ctose. Elution from DE-52 columns showed that the relative abundance o f the six activities changes, depending on the organ and on the develo pmental stage. FK1 and FK2 were present at high activities in tubers b ut at very low activity in leaves; conversely FK3 was present at very low activity in tubers but at high activity in leaves. During storage of potato tuber, and also during sprouting, there was a decrease of FK 1 and FK2. In contrast, glucose-phosphorylating activity was very low in growing tubers. During storage and sprouting the activity of the gl ucose-phosphorylating enzymes rose, until they exceeded FK1 and FK2. T his was due particularly to an increase of HK1, whereas HK2 declined r elative to HK1, and HK3 was always negligible. These changes in the pa ttern of hexose-phosphorylating enzyme forms are compared with the cha nging metabolic fluxes and pools of hexose sugars in potato tubers. It is concluded that organ- and development-specific changes in the abun dance of the various enzyme forms contribute to the regulation of hexo se metabolism in the potato.