Complex formation between methylamine dehydrogenase and amicyanin from Paracoccus denitrificans.

Two proteins isolated from Paracoccus denitrificans, the copper-containing electron carrier amicyanin and the pyrroloquinoline quinone-containing enzyme methylamine dehydrogenase, have been shown to form a complex. Complex formation between methylamine dehydrogenase and either oxidized or reduced amicyanin resulted in alterations in the absorbance spectrum of the pyrroloquinoline quinone prosthetic group of methylamine dehydrogenase. Binding of amicyanin to the enzyme exhibited positive cooperativity. Complex formation with methylamine dehydrogenase shifted the oxidation-reduction midpoint potential of amicyanin by 73 mV, from +294 to +221 mV, making electron transfer from amicyanin to cytochrome c551 (Em = +190 mV) thermodynamically possible.