Abstract
The resolution of a membrane-bound quinoprotein alcohol dehydrogenase (ADH), a key enzyme in vinegar making, was examined in Gluconobacter suboxydans. ADH in membranes of the organism was found to be converted to the apo-form, which is free from pyrroloquinoline quinone (PQQ), during cultivation or incubation at acid pH. The apoenzyme appeared at the stationary phase when cells were grown in medium exhibiting an acid pH at the end of the cultivation. The incubation of resting cells containing the holoenzyme in acid buffer also caused apoenzyme formation. On the other hand, the enzyme in cells grown or incubated at neutral pH was almost all of the holo-form. The apoenzyme was reactivated by exogenous PQQ and calcium ions. Of the tested metal ions, only the calcium ion was effective. The recovery of ADH activity was attained on incubation of the apoenzyme with PQQ and calcium ions at pH 6.0 and 25°C for 10 min.
