Measurements of Oxidoreductase-like Activity of Intact Bacterial Cells by an Amperometric Method Using a Membrane-Coated Electrode

The oxidation of D-glucose and nicotinic acid by intact cells of Gluconobacter industrious and Pseudomonas fluorescens, respectively, is successfully measured by an amperometric method using such compounds as Fe(CN)6(3-), p-benzoquinone, and dichlorophenolindophenol as electron acceptors. Analysis of the experimental results reveals that the intact cells behave like oxidoreductases whose kinetics follows a Michaelis-Mententype equation. The catalytic behavior is explained by a model which treats the bacterial cells as bags of enzymes and assumes distribution equilibrium in the concentrations of both the substrate and the electron acceptor between the test solution and the medium within the cells. The catalytic activity can be characterized by three quantities: the maximum reaction rate (vB) and the ratios of the Michaelis constant to the distribution constant for the substrate (Ks,cell/Ks,p) and to that for the electron acceptor (KM,cell/KM,p). Advanced modification of the model to involve the membrane permeability reveals that the three quantities are effective for explaining the catalytic behavior even when the permeability effect is significant. Thus, the three quantities should be regarded as the parameters which can reflect the permeability effect.