An alternative scaling approach such as the total quasi-steady-state assumption can be utilized to analyze enzyme catalyzed reactions, see for example , , and . In this work, we focused our attention to the scaling approach of the standard QSSA, and singular perturbation analysis to derive asymptotic approximations to the dynamics of the coupled enzyme assays. Our analysis outlines a procedure to estimate higher order corrections to estimate the error of approximations, and our approach can be extended to a variety of coupled enzyme catalyzed assays, including enzyme catalyzed reactions with more reaction steps.