Redox regulation of glucitol dehydrogenase from peach fruits

MATÍAS D. HARTMAN; CARLOS M. FIGUEROA; ALBERTO A. IGLESIAS

Puerto Madryn, Argentina

Congreso; XLVI Reunión Anual de la SAIB; 2010

Sociedad Argentina de Investigación en Bioquímica y BM

Glucitol (Gol) is a major photosynthate in plants from the Rosaceae family. This polyol is synthesized in mature leaves and then translocated to heterotrophic tissues, such as fruits and young leaves, where it is converted into fructose in a reaction catalyzed by Gol dehydrogenase (GolDHase, EC 1.1.1.14). Despite the importance of this enzyme for carbon partitioning in these plants, little is known about its regulation. Therefore, we cloned the gene encoding for GolDHase from peach (Prunus persica) fruits (PpeGolDHase) and expressed it in Escherichia coli cells. Kinetic parameters obtained with the recombinant protein were similar to those reported for the enzyme purified from apple and pear fruits. PpeGolDHase was inhibited by Cu2+, Hg2+, Ni2+ and Zn2+, with I0.5 of 0.031, 0.096, 15.8 and 43.9 μM, respectively. Loss of activity was observed when PpeGolDHase was incubated with diamide, H2O2 and oxidized glutathione (k´´ values were 12.3, 6.93 and 0.086 M-1s-1, respectively). Interestingly, the activity of the oxidized enzyme was recovered by reduction with thioredoxin (from E. coli and wheat leaf) and reduced glutathione. Considering that Gol accumulation has been related with abiotic stress tolerance, we hypothesized that PpeGolDHase could be inhibited under oxidative stress, thus maintaining levels of Gol high enough to exert a protective role as a hydroxyl-radical scavenger.