Partial purification from potato tubers of three fructokinases and three hexokinases which show differing organ and developmental specificity
1993
Renz, A. | Merlo, L. | Stitt, M.
A combination of chromatography on DE-52 cellulose, Cibacron Blue agarose, Mono Q anion exchanger and gel filtration was used to resolve different hexose-phosphorylating enzymes from growing "sink" potato tubers (Solanum tuberosum L.). Three enzymes fructokinases: FK1, FK2 and FK3) are active with fructose and inactive with glucose, and three (hexokinases: HK1, HK2 and HK3) are active with glucose but not with fructose. Elution from DE-52 columns showed that the relative abundance of the six activities changes, depending on the organ and on the developmental stage. FK1 and FK2 were present at high activities in tubers but 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 FK1 and FK2. In contrast, glucose-phosphorylating activity was very low in growing tubers. During storage and sprouting the activity of the glucose-phosphorylating enzymes rose, until they exceeded FK1 and FK2. This was due particularly to an increase of HK1, whereas HK2 declined relative to HK1, and HK3 was always negligible. These changes in the pattern of hexose-phosphorylating enzyme forms are compared with the changing metabolic fluxes and pools of hexose sugars in potato tubers. It is concluded that organ- and development-specific changes in the abundance of the various enzyme forms contribute to the regulation of hexose metabolism in the potato.
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