Characteristics necessary for an interconvertible enzyme cascade to generate a highly sensitive response to an effector.

摘要: A monocyclic interconvertible enzyme cascade, in which active and inactive states of an are interconverted by two opposing enzyme-catalysed reactions, does not necessarily produce a greater degree sensitivity to effector than one could expect from direct interaction between target reaction. On the contrary, cascade acts on enzymes catalysing interconversion reactions altering apparent value its specificity constant will always generate less sensitive response would give. Nonetheless, even if both obey Michaelis-Menten kinetics with ordinary types inhibition activation, can easily enormous 0.5% change concentration increase proportion state 10% 90%: this corresponds approximately Hill coefficient 800. To maximize sensitivity, following conditions must be satisfied: (1) modifier act under near saturation; (2) them opposite directions; (3) it alter values their catalytic constants; (4) subject respond at much lower concentrations activation. As last these appears counter-intuitive, suggests that feeble activation real systems may have passed unnoticed, or been dismissed as physiologically insignificant, although reality crucial effective system.