Open AccessCharacterization and Partial Purification of Aldose-6-phosphate Reductase (Alditol-6-Phosphate:NADP 1-Oxidoreductase) from Apple Leaves
Author(s) -
Fayek B. Negm,
Wayne H. Loescher
Publication year - 1981
Publication title -
plant physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.554
H-Index - 312
eISSN - 1532-2548
pISSN - 0032-0889
DOI - 10.1104/pp.67.1.139
Subject(s) - aldose reductase , oxidoreductase , aldehyde reductase , phosphate , chemistry , biochemistry , reductase , enzyme , chromatography
Aldose-6-phosphate reductase (alditol 6-phosphate:NADP 1-oxidoreductase) was isolated and characterized from mature apple leaves (Malus domestica cv. Starkrimson). The enzyme was purified 79-fold. The enzyme catalyzed the following reversible reaction: d-glucose 6-phosphate + NADPH + H(+) right arrow over left arrow d-sorbitol 6-phosphate + NADP(+). No activity was detected when NAD(+) was substituted for NADP(+) or when NADH was substituted for NADPH. The enzyme reduced d-galactose 6-phosphate at a higher rate than d-glucose 6-phosphate. d-Mannose 6-phosphate and 2-deoxy-d-glucose 6-phosphate were reduced at low rates. d-Glucose 1-phosphate, d-fructose 6-phosphate, d-ribose 5-phosphate, d-glucose, and sorbitol did not serve as substrates. The pH optimum for both d-sorbitol 6-phosphate oxidation and d-glucose 6-phosphate reduction was 9.5. The K(m) values for d-sorbitol 6-phosphate oxidation and d-glucose 6-phosphate reduction were 3.9 and 20 millimolar, respectively. AgNO(3) (0.1 millimolar) and p-chloromercuribenzoate (1.0 millimolar) completely inhibited the enzyme.Aldose-6-phosphate reductase activity was also detected in mature leaves from Golden Delicious and Antonovka apples (Malus domestica), Conference and Bartlett pears (Pyrus communis), Redhaven peach (Prunus persica), and Perfection apricot (Prunus armeniaca). This suggests that the enzyme has a wide distribution and plays an important role in sorbitol synthesis.