Apparent co-operativity for highly concentrated Michaelian and allosteric enzymes.

The effect of high enzyme concentration on velocity curves is analysed quantitatively for both Michaelian and simple allosteric enzymes. The general principles and practical approaches developed here are applicable to other models and may provide information on enzyme function in vivo. At physiological enzyme concentrations. Michaelian enzymes display amplification properties of the same magnitude as those observed for allosteric enzymes. In terms of apparent co-operativity, this corresponds to Hill coefficients that are locally much larger than the number of interacting or non-interacting binding sites. However, compared to the Michaelian case, allosteric interactions are needed to provide a combination of both positive and negative apparent co- operativities . These effects are important for understanding the biological significance of intersubunit cooperation in oligomeric enzymes.