When an enzyme catalyzed reaction of primary interest cannot be observed experimentally, enzymologists indicator the substrate depletion or product accumulation by linking the reaction catalyzed by the primary enzyme to one or more (indicator) enzyme-catalyzed reactions. If the linked reaction can be observed experimentally, then it is theoretically possible to investigate the kinetic behavior of the non-observable reaction of primary interest. As a case study, we carried out a kinetic analysis of the coupled (or auxiliary) enzyme reaction (1)-( ). The two most important results of our analysis are: