The primary contributions of this paper are the estimation of scaling vari- QSSA without justification . Moreover, previous analyses have only employed PFO kinetic models, and do not provide insight as to how to properly estimate kinetic timescales via nonlinear methods, even though reaction mechanism of zymogen activation is inherently nonlinear. This work outlines a clear procedure for estimating depletion timescales, and serves as a template for the analysis of more complicated reactions. We give a brief summary of the results of the analysis in what follows.