Involved in the biosynthesis of validamycin B, a component of the antifungal and antibiotic validamycin complex used as a crop protectant. Catalyzes the regioselective hydroxylation of validamycin A (4-O-beta-D-glucopyranosyl-validoxylamine A) at the C-6 position to yield validamycin B. To a lesser extent, also able to convert validoxylamine A to its hydroxylated derivative. 2-oxoglutarate + O2 + validamycin A = CO2 + H(+) + succinate + validamycin B 2-oxoglutarate + O2 + validoxylamine A = CO2 + H(+) + succinate + validoxylamine B Binds 1 Fe(2+) ion per subunit. kcat is 0.97 min(-1) for validamycin A as substrate (at pH 7.2). Optimum pH is 7.2. Antibiotic biosynthesis. Cells lacking this gene are still able to produce the aminoglycoside antibiotic validamycin A, but not validamycin B. Belongs to the iron/ascorbate-dependent oxidoreductase family.