Lactose and D-galactose metabolism in Staphylococcus aureus. IV. Isolation and properties of a class I D-ketohexose-1,6-diphosphate aldolase that catalyzes the cleavage of D-tagatose 1,6-diphosphate.

The inducible D-ketohexose-1,6-diphosphate aldolase that functions in the metabolism of lactose and D-galactose in Staphylococcus aurues was purified to electrophoretic homogeneity from an extract of D-galactose-grown cells. At saturating substrate concentrations, D-tagatose 1,6-diphosphate was cleaved to dihydroxyacetone phosphate plus D-glyceraldehyde 3-phosphate at twice the rate of D-fructose 1,6-diphosphate; Km values for D-tagatose 1,6-diphosphate and D-fructose 12,6-diphosphate were 1.5 mM and 2.5 mM, respectively. The enzyme catalyzed the aldol condensation of dihydroxyacetone phosphate and D-glyceraldehyde 3-phosphate to yield a mixture of the 1,6-diphosphate derivatives of D-tagatose, D-fructose, D-sorbose, and D-psicose, indicating that it also catalyzes the cleavage of all four D-2-ketohexose 1,6-diphosphates. The enzyme was not inhibited by EDTA and it had no divalent metal ion requirement, but it did exhibit substrate-dependent inactivation by NaBH4, indicating that it is a Class I (Schiff's base) aldolase. Density gradient centrifugation and gel electrophoresis in the presence of sodium dodecyl sulfate indicated that the enzyme exists as a monomer with amolecular weight of about 37,000 and a sedimentation coefficient of 3.4 S. Data on the stability, pH optimum, and inducibility of the enzyme are also presented.