Catalyzes the NAD-dependent oxidation of glycerol to dihydroxyacetone (glycerone). Allows microorganisms to utilize glycerol as a source of carbon under anaerobic conditions. In E.coli, an important role of GldA is also likely to regulate the intracellular level of dihydroxyacetone by catalyzing the reverse reaction, i.e. the conversion of dihydroxyacetone into glycerol. Possesses a broad substrate specificity, since it is also able to oxidize 1,2-propanediol and to reduce glycolaldehyde, methylglyoxal and hydroxyacetone into ethylene glycol, lactaldehyde and 1,2-propanediol, respectively. glycerol + NAD(+) = dihydroxyacetone + H(+) + NADH Binds 1 zinc ion per subunit. Inhibited by Cu(2+). The catalytic efficiency of the reverse reaction (dihydroxyacetone reduction) is more than 100-fold higher than that of the forward direction (glycerol oxidation). Optimum pH is 5.5-6.0 for dihydroxyacetone reduction and 9.5-10.0 for glycerol oxidation. Polyol metabolism; glycerol fermentation; glycerone phosphate from glycerol (oxidative route): step 1/2. Homodimer and homooctamer. Expression is higher during stationary phase than during logarithmic growth. Full expression of gldA is achieved by induction with hydroxyacetone and stationary-phase growth conditions. Belongs to the iron-containing alcohol dehydrogenase family. Extended N-terminus.