Difference Between Heme and Hemin

The key difference between heme and hemin is that heme contains ferrous ion, whereas hemin contains ferric ion.

Heme and hemin are porphyrin protein molecules. These are heterocyclic macromolecules that we can name organic compounds.

CONTENTS

1. Overview and Key Difference
2. What is Heme 
3. What is Hemin
4. Similarities Between Heme and Hemin
5. Side by Side Comparison – Heme vs Hemin in Tabular Form
6. Summary

What is Heme?

Heme is a biochemical substance that is necessary to bind oxygen in the bloodstream. This substance is produced from biosynthesis in both the bone marrow and the liver. In the field of microbiology, the term heme refers to a coordination complex containing an iron ion coordinated to a porphyrin that acts as a tetradentate ligand and to one or two axial ligands.

Generally, hemoproteins, including heme, have many biological functions, such as the transportation of diatomic gases, chemical catalysis, diatomic gas detection, and electron transfer. Heme iron acts as a source of or sink of electrons during electron transfer or redox chemistry.

There are different types of heme molecules such as heme A, heme B, heme C, and heme O. These molecules have different chemical formulas and different functional groups as well. Among these types, heme B is the most common form, but heme A and heme C are also equally important. In addition, there can be some rare forms of heme as well, which include heme I, which is a derivative of heme B that covalently attaches to the protein residue of lactoperoxidase. Similarly, heme M is derived from heme B, which tends to covalently bond to the active site of myeloperoxidase. Heme D is also a derivative of heme B, consisting of a propionic acid side chain at the C-6 position.

When considering the production of heme proteins, the enzymatic pathway of heme production is named the porphyrin synthesis, and here all the intermediates are tetrapyrroles that are chemically named as porphyrins.

The degradation of heme protein molecules begins inside the macrophages of the spleen, which can remove old and damaged erythrocytes from the circulation.

What is Hemin

Hemin is a type of porphyrin containing chlorine, and it can form from heme groups, including heme B. This compounds’ structure is named protoporphyrin IX, and it contains a ferric iron ion containing a coordinating chloride ligand. In chemical terms, the hemin molecule is different from heme-compound hematin because of the chloride ion in hemin in the place of the coordinating hydroxide ion in hematin.

This substance is produced in our human body endogenously, e.g. during the turnover of old red blood cells. However, this substance can also form as a result of hemolysis or vascular injury. Moreover, several proteins in human blood also bind to hemin, e.g. hemopexin and serum albumin.

What are the Similarities Between Heme and Hemin?

• Heme and hemin are organic compounds.
• Both are coordination complexes.
• They contain iron ions.

What is the Difference Between Heme and Hemin?

Heme and hemin are porphyrin protein molecules. Heme is a biochemical substance that is necessary to bind oxygen in the bloodstream while hemin is a type of porphyrin containing chlorine that can form from heme group, including heme B. The key difference between heme and hemin is that heme contains ferrous ion, whereas hemin contains ferric ion. Besides, heme does not contain chloride atoms, while hemin contains chloride atoms.

Below is a summary of the difference between heme and hemin in tabular form.

Summary – Heme vs Hemin

Heme and hemin are porphyrin protein molecules. The key difference between heme and hemin is that heme contains ferrous ion, whereas hemin contains ferric ion. Furthermore, hemin molecules contain chloride atoms in the chemical structure, whereas heme does not contain chloride atoms.

Reference:

1. Nordquist, Richard. “Theme.” ThoughtCo, Feb. 16, 2021, Available here.

Image Courtesy:

1. “Mboxygenation” By Smokefoot – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Hemin edit1” By Impz – Own work (CC BY 3.0) via Commons Wikimedia