Soluble glucose dehydrogenase (sGDH) is a homodimeric quinoprotein found in Acinetobacter calcoaceticus , that effectively catalyzes the oxidation of aldose sugars to their corresponding aldonolactones, for example, glucose to gluconolactone. Each monomer subunit requires two Ca<sup>2+</sup> for dimerization and one Ca<sup>2+</sup> for PQQ's functional activity. The steady-state kinetics study of sGDH exhibits cooperativity. The observed cooperativity could originate from conformational changes in one subunit of the enzyme, for example, in the steady-state presence of a substrate, an intermediate, or a product, which would induce changes in the second subunit, consequently, the enzymatic activity. We have synthesized adducts mimicking the intermediate of the enzymatic reaction--acetone hemiketal, ethylenethiol, ethyleneglycol and methanol ketals. Fluorimetry has shown that hemiketals exhibit fluorescence at 460nm and 480nm. This was observed in both PQQ in water and the acetone hemiketal. The ethylenethiol, ethyleneglycol and methanol ketals show ketal fluorescence occurring around 350nm. We are currently exploring purification methods to isolate the adducts. Once the adducts are purified, their effects on sGDH steady-state kinetics will be studied by reconstituting the apoenzyme with a mixture of PQQ and PQQ adduct.