Modification of an inhibition curve to account for effects of a second compound.

Three methods are proposed for modifying a logistic inhibition curve for a primary compound to account for the role of a second compound. The assumptions underlying each of the three resulting models-similar joint action, multiplicative, and modification-are discussed. The models are compared and model selection procedures are given. An example is presented in which the inhibiting effect ofp-coumaric acid on the growth of morning-glory plants is modified by the addition of glucose.