In this section we again consider the extreme cases when the indicator reaction is very fast or very slow in comparison to the non-observable reaction for the zymogen activation coupled to its enzyme catalyzed reaction. As mentioned, the major difference between the zymogen activation coupled to its enzyme catalyzed reaction and the coupled auxiliary reaction mechanism is that, while the indicator reaction for the coupled auxiliary enzyme assay cannot complete before the non-observable reaction, the completion of the secondary reaction can occur before or after the completion of the primary reaction.