How to reveal various aspects of regulation in group-transfer pathways

AbstractFor an ‘ideal’ metabolic pathway, genetic modulation of the enzyme concentration and titration with different types of specific inhibitor all leads to the determination of the same quantitative indicator of the extent to which an enzyme controls the flux and metabolite concentrations: the control coefficient with respect to the enzyme concentration. By contrast, for a group-transfer pathway these methods reveal various modes of the control exerted by an enzyme on the flux and on the concentrations of pathway components. Modulation of gene expression allows one to determine the (classical) control coefficient with respect to the enzyme concentration. Titration with inhibitors (competitive or uncompetitive) that do not bind to enzyme-enzyme complexes leads to information on the classical control coefficient of the inhibited enzyme and on the relative concentrations of its different forms. Should such inhibitors be irreversible, the classical control coefficients can be measured directly. Titration with a purely non-competitive inhibitor (binding to all the complexes of the target enzyme) reveals the impact control coefficient, a measure of the total kinetic effect of that enzyme on the system. Combined approaches applied to intact systems will detect an expected variety of control properties that cannot be measured after the system has been disassembled