Partial Purification and Characterization of d-Ribose-5-phosphate Reductase from Adonis vernalis L. Leaves.
This study presents evidence for a new enzyme, d-ribose-5-P reductase, which catalyzes the reaction: d-ribose-5-P + NADPH + H(+) --> d-ribitol-5-P + NADP(+). The enzyme was isolated from Adonis vernalis L. leaves in 38% yield and was purified 71-fold. The reductase was NADPH specific and had a pH optimum in the range of 5.5 to 6.0. The Michaelis constant value for d-ribose-5-P reduction was 1.35 millimolar. The enzyme also reduced d-erythrose-4-P, d-erythrose, dl-glyceraldehyde, and the aromatic aldehyde 3-pyridinecarboxaldehyde. Hexoses, hexose phosphates, pentoses, and dihydroxyacetone did not serve as substrates. d-Ribose-5-P reductase is distinct from the other known ribitol synthesizing enzymes detected in bacteria and yeast, and may be responsible for ribitol synthesis in Adonis vernalis.
Negm
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Department of Floriculture and Ornamental Horticulture, Cornell University, Ithaca, New York 14853.
Marlow
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GC