has detection method has measured entity has substrate has function has participant catalytic activity luminescence method Luciferin 4-monooxygenase Adenosine triphosphate substrate coupled enzyme activity measurement method ATP coupled enzyme activity measurement method The effect of a perturbagen on an enzyme activity is coupled to a secondary signal. The activity of an enzyme, e.g. luciferase is limited by the availability of one of its substrates, namely, ATP, which is coupled to the activity of another enzyme, e.g. a kinase, ATPase, etc. beetle luciferin