Figure 9. Schematic illustration of the possible functioning of PDHC semisaturated with thiamine pyrophosphate and influence of anti-coenzyme derivatives on enzyme activity.

Partial dissociation of the endogenous thiamine pyrophosphate in the absence of substrate allows the binding of anti-coenzyme derivative and inhibition of enzyme in the case of semisaturated as well as saturated concentration of coenzyme. Some anti-coenzyme binding often occurs with the same or even greater affinity in comparison with native coenzyme. Addition of substrate to the enzyme with partially dissociated coenzyme caused reassociation of coenzyme and activation of complex. Addition of substrate to the enzyme containing partially dissociated coenzyme and anti-coenzyme did not cause reactivation of enzyme.