Question

Free heme in aqueous solution when exposed to dioxygen is finally converted to (circle around iron in the given choices represents the protoporphyrin IX)

• A.
• B.
• C.
• D.

Answer 1

The Correct Option is D

To solve this problem, we need to understand the chemistry of heme and its interaction with dioxygen (O₂), which results in the oxidation of iron at the center of the heme structure. Let's break down the steps:

Step 1: Understanding Free Heme

Heme is an iron-containing compound found in hemoglobin, and its structure can be simplified as an iron (Fe) atom inserted in a large heterocyclic organic ring called a porphyrin. In biological systems, this is usually protoporphyrin IX.

Step 2: Interaction with Dioxygen

In aqueous solution, when free heme is exposed to dioxygen, the iron(II) (Fe²⁺) in the heme can interact with O₂. In this process, the iron gets oxidized from Fe²⁺ to Fe³⁺, and the formation of a less reactive compound follows.

Step 3: Conversion to the Final Product

This oxidation process leads to the formation of a stable ferric heme compound known as hemin. Hemin retains the same porphyrin structure with iron now in the +3 oxidation state. The correct representation of this compound in the provided options is:

The conversion of Fe²⁺ to Fe³⁺ in the presence of dioxygen is a fundamental reaction in the field of bioinorganic chemistry, detailing essential transformations within the body and laboratory settings.

Conclusion

The free heme in aqueous solution is finally converted to hemin upon exposure to dioxygen. Hemin is the oxidized form of heme where the iron is in the +3 oxidation state, corresponding to the fourth option given.