Does anyone know what the electrons and protons are when the mass changes to 135 on caesium?

Protons are still going to be 55 and electrons will be 55.

Explanation:

The number of electrons and protons is the same unless the atom is an ion, which we can assume it isn't. The only thing that affects the total atomic mass is what's inside the nucleus (protons and neutrons), and if the number of protons stayed the same (or the element did not change), then the only thing that changed was the neutrons, therefore the protons and electrons are still the same as they would be if it were a normal Cesium atom.

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.