Soluble glucose dehydrogenase (sGDH) is a homodimer that requires one pyrroloquinoline quinone (PQQ) and two Ca2+ cations per monomer subunit, to oxidize aldoses. The steady-state kinetics study of sGDH exhibits cooperativity at a high substrate concentration. The observed cooperativity could originate from conformational changes in one subunit of the enzyme, for example, in the steady-state presence of a substrate, intermediate, or product which would induce changes in the second subunit, consequently, the enzymatic activity. A recently proposed mechanism for methanol dehydrogenase, a quinoprotein that oxidizes methanol, indicates that a PQQ-methanol intermediate may play a part in determining kinetic behavior. Our approach focuses upon (1) the synthesis of a PQQ adduct mimicking an intermediate of PQQ during the enzymatic reaction and the examination of the kinetic behavior of partially reconstituted sGDH with the adduct, and (2) the study of the steady-state kinetics of sGDH in the presence of a substrate or product analog.