As mentioned previously, the theoretical reduction analysis of zymogen activation reactions has been limited to PFO models . Such models have limited validity in time course experiments , and the aim of this work is first and foremost to take a necessary "first step" in the nonlinear analysis of such reactions. First, we will introduce proper scaling techniques that can be employed in a general methodology to more complicated reactions. In Section 3 we will show how to estimate timescales based on these scaling methods, and we will formulate a reduced model from the analysis of these timescales (Section 4). The reduced model admits closed-form solutions in the form of a Schnell-Mendoza equation , and conditions for the validity of the model will be established. In addition, we will exploit the geometry of the mathematical structure in extreme situations when the speeds of the reactions are significantly disparate. This will allow us to "simplify" the reduced model and obtain asymptotic solutions that are essentially less complicated (in form) than both the general reduced model and the system of mass action equations. Finally, in Section 7, we conclude with a brief discussion of the results and their relevance in possible future work involving the inverse problem.