Hemoredox

Hemoredox is the study of redox chemistry centered on heme, the iron-containing porphyrin prosthetic group found in many proteins. It encompasses how the iron atom cycles between the ferrous (Fe2+) and ferric (Fe3+) states during electron transfer, catalysis, and ligand binding. The redox potential of a heme site is modulated by the protein environment, axial ligands, and the presence of ligands such as O2, CO, or NO, leading to a wide range of redox behavior across heme proteins.

In biology, hemoredox covers the roles of heme in energy metabolism and biotransformations. Electron transfer chains use cytochromes to shuttle electrons; other heme proteins bind or release O2 (hemoglobin, myoglobin) and participate in reactive oxygen species management. Heme-dependent enzymes such as cytochrome P450 monooxygenases, peroxidases, and catalases use redox cycling of Fe to activate substrates or detoxify peroxides. Heme redox also participates in signaling and in processes such as heme degradation by heme oxygenase, which releases iron, biliverdin, and carbon monoxide.

Techniques to study hemoredox include UV–visible spectroscopy to monitor changes in the Soret band, electron paramagnetic resonance (EPR) for ferric states, Mossbauer spectroscopy for iron environments, and various redox titration methods. Structural context from X-ray crystallography and cryo-EM helps relate redox properties to protein function. Researchers also use chemical or protein-based redox mediators to probe electron-transfer pathways.

Significance and applications include understanding metabolic regulation, disease mechanisms linked to redox imbalance or methemoglobinemia, and the design of bioinspired catalysts and biosensors that exploit heme redox properties.