chemistry

Heme B

Heme B is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Heme B rather than just read about it. In short: Heme B or haem B (also known as protoheme IX) is the most abundant heme. Hemoglobin and myoglobin are examples of oxygen transport proteins that contain heme B.

Key takeaways

Heme B belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Heme B to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Heme B from memory before moving on to harder problems.

Reference excerpt

Heme B or haem B (also known as protoheme IX) is the most abundant heme. Hemoglobin and myoglobin are examples of oxygen transport proteins that contain heme B. The peroxidase family of enzymes also contain heme B. The COX-1 and COX-2 enzymes (cyclooxygenase) of recent fame, also contain heme B at one of two active sites. Isolated heme B is slightly soluble in ammonia water and is extremely sensitive to oxygen, instantly oxidizing to a dark green to black-brown color when exposed to air. Generally, heme B is attached to the surrounding protein matrix (known as the apoprotein) through a single coordination bond between the heme iron and an amino-acid side-chain. Both hemoglobin and myoglobin have a coordination bond to an evolutionarily-conserved histidine, while nitric oxide synthase and cytochrome P450 have a coordination bond to an evolutionarily-conserved cysteine bound to the iron center of heme B. Since the iron in heme B containing proteins is bound to the four nitrogens of the porphyrin (forming a plane) and a single electron donating atom of the protein, the iron is often in a pentacoordinate state. When oxygen or the toxic carbon monoxide is bound the iron becomes hexacoordinated. The correct structures of heme B and heme S were first elucidated by German chemist Hans Fischer.

Chemical properties

Heme B can be prepared by reducing Hemin in pyridine with sodium dithionite. Upon addition of the dithionite, the solution changed color and gelled:

It can also be prepared by reducing Hemin with Raney nickel in ammonia water:

Degradation

In humans, heme B is degraded by the enzyme heme oxygenase to give biliverdin, which is then converted to bilirubin by biliverdin reductase.

Bilirubin is either rendered water soluble by forming bilirubin diglucuronide and excreted from the liver in bile, or further reduced to urobilinogen.

References

Illustrations

Worked examples

Example 1 — a first encounter with Heme B

Start with the simplest possible case. Write down what Heme B claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Heme B before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Heme B ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Heme B

In research: Heme B appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Heme B in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Heme B is common in secondary-school and first-year university syllabi. It links to neighbouring topics Biomolecules, Tetrapyrroles, so understanding it makes those chapters shorter.
In everyday life: Look for Heme B outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Heme B in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Heme B means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Heme B out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Heme B in simple terms?

Heme B or haem B (also known as protoheme IX) is the most abundant heme. Hemoglobin and myoglobin are examples of oxygen transport proteins that contain heme B.

Why does Heme B matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Heme B?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Heme B.