Mathematical modeling of an Enzyme-Catalyzed Substrate Conversion usually leads to very large scale Continuous-Time Markov Chains (CTMC). If reaction rates in the conversion are different in orders of magnitude, the analysis of the model will require solving a stiff Ordinary Differential Equation (ODE) which is computationally expensive. One way to avoid the complexity of the exact model is to utilize an approximation (aggregation) technique to make the exact model smaller and non-stiff. In this work, we compare two general aggregation techniques, one based on system partitioning and, the other based on Michaelis-Menten Approximation. Results demonstrate the improvements of our proposed method based on system partitioning in terms of accuracy over Michaelis-Menten Approximation.