Specific transfer of 3H from D-[3-3H]gluconic acid into L-tartaric acid in vitaceous plants.

Transfer of 3H from D-gluconic acid, specifically labelled with 3H at C-2 or C-3 and 14C at C-1, C-2, or C-3, 4, to L(+)-tartaric acid was examined in leaves and berries of Vitis labrusca cv Delaware and in leaves of Parthenocissus quinquefolia. 3H located at C-3 of D-gluconic acid was highly conserved in this transfer, yielding a 3H/14C ratio between 3.3 and 14 in the light and between 11 and 22 in the dark. These experiments strongly suggest that a portion of the 3H present in L(+)-tartaric acid may have been transferred from D-gluconic acid to L(+)-tartaric acid, possibly via NADP[3H] through a redox process involving reduction of L-xylo-2-hexulosonate (2-keto-L-idonate). Both [3H]-tartaric acid and [14C]tartaric acid synthesized in grape leaves from D-[3-3H, 2-14C]gluconic acid, or [3-3H, 3,4-14C]gluconic acid were characterized as L(+)-chiral form exclusively, the naturally occurring from of tartaric acid.