Potato (Solanum tuberosum L.) fructokinase expressed in yeast exhibits inhibition by fructose of both in vitro enzyme activity and rate of cell proliferation

A cDNA clone of potato (Solanum tuberosum) fructokinase (EC 2.7.1.4) was expressed in mutant yeast cells unable to phosphorylate, or grow on either glucose or fructose. The transformed yeast cells complemented growth on fructose but not on glucose. Crude protein extracts of the transformed yeast showed phosphorylation activity with fructose as substrate, but not with glucose. In addition, in vitro enzyme activity was substrate inhibited at fructose concentrations above 2 mM. Proliferation of the transformed yeast cells was also inhibited by increasing fructose concentrations, indicating that the phenomenon of substrate inhibition may occur in vivo. These data suggest that substrate inhibition of fructokinase in potato tubers is a physiologically significant phenomenon. (C) 1997 Elsevier Science Ireland Ltd.