Jeremy Gunawardena

Ultrasensitivity, or an input-output response which is "steeper" than
hyperbolic, was first noticed in the response of allosteric enzymes to
metabolic regulators. It enables large changes in flux rates to be
controlled by relatively small changes in metabolite
concentrations. Its significance in signalling is quite
different. I'll explain why an ultrasensitive mechanism seems to be a
necessary component of any decision making system. What do these
mechanisms look like? There is evidence that some MAP kinase cascades
can implement an ultrasensitive response and that this underlies the
decisions made by the corresponding signalling pathway. Simulations
show that this ultrasensitivity emerges from basic properties of
protein phosphorylation. I'll discuss a simplified ("crude") model of
this, which can be studied analytically, to see if we can get some
intuition for how it works and how it might be used biologically.