It is also a buffer, which means that it resists pH change.
Such differences are likely due to pH changes or differences in primary structure of the luciferase.
They all can be changed a bit by big pH changes.
This results in a greater pH change and a proportionally greater electronic signal.
If the pH changes, things like this, then watch with a meter.
Halochromism occurs when a substance changes color as the pH changes.
You should see the pH changes in a memorable way.
The 0.1 pH change means there are now 30 percent more hydrogen ions in the water.
It would be difficult to establish a biological origin without first showing that a pH change caused didn't cause your observations.
Conversely, when you know you are in a part of a curve where pH changes slowly, using larger additions can save time.