The structure of L-fuculose-1-phosphate aldolase in a cubic crystal form has been determined with and without the inhibitor phosphoglycolohydroxamate at 2.4 and 2.7 angstrom (1 angstrom = 0.1 nm) resolution, respectively. This inhibitor mimics the enediolate transition state of the substrate moiety dihydroxyacetone phosphate. The structures showed that dihydroxyacetone phosphate ligates the zinc ion of this metal-dependent class II aldolase with its hydroxyl and keto oxygen atoms, shifting Glu73 away from the zinc coordination sphere to a non-polar environment. At this position Glu73 accepts a proton in the initial reaction step, producing the enediolate which is then stabilized by the zinc ion. The other substrate moiety L-lactaldehyde was modeled, because no binding structure is yet available.