The 9-carboxyl group of pyrroloquinoline quinone, a novel prosthetic group, is essential in the formation of holoenzyme of D-glucose dehydrogenase.

Availability of different analogues of pyrroloquinoline quinone as the prosthetic group for apo-D-glucose dehydrogenase was examined. The 9-carboxyl group of pyrroloquinoline quinone was shown to be essential for the reconstitution of the enzyme activity. Although the carboxyl group may not be involved in catalytic function, it is quite probable to contribute the binding of the prosthetic group to apoenzyme.