Mediated bacterial electrocatalysis is used to follow the activation process of ape-glucose dehydrogenase in Escherichia coli cells. A catalytic current is produced at an electrode modified with the bacterial cells when pyrroloquinoline quinone (PQQ) is added to the test solution containing glucose and an electron acceptor. The current is due to the catalytic action of hole-glucose dehydrogenase which is formed from the ape-enzyme with externally added PQQ The catalytic current measurements reveal that the rate of incorporation of PQQ into the enzyme in the bacterial cells depends on the PQQ concentration in the sample solution and that magnesium ions have a significant effect on the hole-enzyme formation.