D-mannose, D-xylose, D-galactose, 2-deoxy-D-glucose and L-arabinose will function as aldose substrates, but with low affinities. The ketose substrate must be in the open-chain form. The apparent affinity for fructose is low, because little of the fructose substrate is in the open-chain form. Xylulose and glycerone (dihydroxyacetone) will replace fructose, but they are poor substrates. The enzyme from Zymomonas mobilis contains tightly bound NADP+.
