chemistry

Heme C

Heme C 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 C rather than just read about it. In short: Heme C (or haem C) is an important kind of heme. History The correct structure of heme C was published in mid 20th century by the Swedish biochemist K.-G.

Key takeaways

Heme C 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 C to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Heme C from memory before moving on to harder problems.

Reference excerpt

Heme C (or haem C) is an important kind of heme.

History The correct structure of heme C was published in mid 20th century by the Swedish biochemist K.-G. Paul. This work confirmed the structure first inferred by the great Swedish biochemist Hugo Theorell. The structure of heme C, based upon NMR and IR experiments of the reduced Fe(II) form of the heme, was confirmed in 1975. The structure of heme C including the absolute stereochemical configuration about the thioether bonds was first presented for the vertebrate protein, cytochrome c and is now extended to many other heme C containing proteins.

Properties Heme C differs from heme B in that the two vinyl side chains of heme B are replaced by covalent, thioether linkages to the apoprotein. The two thioether linkages are typically made by cysteine residues of the protein. These linkages do not allow the heme C to easily dissociate from the holoprotein, cytochrome c, compared with the more easily dissociated heme B that may dissociate from the holoprotein, the heme-protein complex, even under mild conditions. This allows a very wide range of cytochrome c structure and function, with myriad c type cytochromes acting primarily as electron carriers. The redox potential for cytochrome c can also be "fine-tuned" by small changes in protein structure and solvent interaction. The number of heme C units bound to a holoprotein is highly variable. For vertebrate cells one heme C per protein is the rule but for bacteria this number is often 2, 4, 5, 6 or even 16 heme C groups per holoprotein. It is generally agreed the number and arrangement of heme C groups are related and even required for proper holoprotein function. For instance, those proteins containing several heme C groups are involved with multiple electron transfer reactions, particularly important is the 6 electron reduction required to reduce atmospheric nitrogen into two organic ammonia molecules. It is common for the heme C to amino acid ratio to be high for bacterial hemeproteins, so the interiors of some cytochrome c proteins appear packed with many heme C groups compared with other hemeproteins. Some hemeproteins, often from single cell organisms, may contain five hemes C. The bc1 complex is another important enzyme that contains a C type heme. The thioether linkages seem to allow a great freedom of function for the holoproteins. In general, the c type cytochromes can be "fine tuned" over a wider range of oxidation-reduction potential than cytochromes b. This may be an important reason why cytochrome c is nearly ubiquitous throughout life. Heme C also plays an important role in apoptosis where just a few molecules of cytoplasmic cytochrome c, which must still contain heme C, leads to programmed cell death. Cytochrome c can be measured in human serum and can be used as a marker for inflammation. In addition to these equatorial covalent bonds, the heme iron is also usually axially coordinated to the side chains of two amino acids, making the iron hexacoordinate. For example, mammalian and tuna cytochrome c contain a single heme C that is axially coordinated to side chains of both histidine and methionine. Perhaps because of the two covalent bonds holding the heme to the protein, the iron of heme C is sometimes axially ligated to the amino group of lysine or even water.

See also Heme Protoporphyrin IX Heme A Heme B Hemeprotein

References

Illustrations

Worked examples

Example 1 — a first encounter with Heme C

Start with the simplest possible case. Write down what Heme C 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 C 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 C 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 C

In research: Heme C 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 C 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 C 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 C 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Heme C” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Heme C in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Heme C 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 C out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Heme C in simple terms?

Heme C (or haem C) is an important kind of heme. History The correct structure of heme C was published in mid 20th century by the Swedish biochemist K.-G.

Why does Heme C 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 C?

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 C.