Existence of a novel prosthetic group, PQQ, in membrane-bound, electron transport chain-linked, primary dehydrogenases of oxidative bacteria.

We have already purified membrane-bound, electron transport-linked, D-glucose dehydrogenase from Pseudomonas jluorescens [I], and found that the enzyme had an unknown prosthetic group differing from NAD(P) and flavin. Furthermore, it appears that alcohol [2], aldehyde [3] and D-glucose [4] dehydrogenases isolated in our laboratory from Gluconobacter suboxydans also have the same prosthetic group. This group’s characteristics closely resembled those of glucose dehydrogenase purified from Acinetobacter [S] and of methanol dehydrogenases from Pseudomonas sp. M27 [6], Rhodopseudomonas acidophila [7] and Hyphomicrobium X [8]. Duine et al. [9] showed recently, that the novel prosthetic group was a pyrrolo-quinoline quinone (PQQ), the structure of which was determined using an X-ray analysis by Salisbury et al. [lo]. To obtain more information on the prosthetic group, we isolated a mutant of P. aeruginosa having less glucose dehydrogenase activity than normal. This activity was shown to be restored by adding the prosthetic group extracted from the purified glucose dehydrogenase of P. fluorescens. Thus, the membrane of the mutant has an apo-glucose dehydrogenase and may be available for the identification of PQQ. Using the mutant membrane, we showed that alcohol, aldehyde and glucose dehydrogenases from G. suboxydans also had the same prosthetic group, PQQ.