Electrospray mass spectrometric study of haem changes during peroxidase denaturation

Electrospray mass spectrometry (ESMS) was used to investigate the denaturation of horseradish peroxidase (HRP) on heating the enzyme under neutral conditions. The rate of loss of the haem signal followed closely the rate of peroxidase inactivation, strongly suggesting that the inactivation of the enzyme was due to haem changes. The results from previous work have indicated that the haem remained protein bound. It was therefore surmised that the haem had formed stronger, perhaps covalent, bonds with the protein during heating.