how haem group acts as an indicator of protein folding?

Answer 1

You should really clarify this question, but if I'm reading it right, there are certain proteins that bind to haem groups. If the protein (hemoglobin, for instance) is folded properly, it will take up the ligand and there will be a change that can be detected by spectrophotometry or fluorimetry, for instance, since the effect of light on the haem changes with whether it is embedded in the protein or is out in the solution.

Answer 2

Oxidation state.