chemistry

Urocanic acid

Urocanic acid 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 Urocanic acid rather than just read about it. In short: Urocanic acid (formally trans-Urocanic acid) is an intermediate in the catabolism of L-histidine. The cis-urocanic acid isomer is rare.

Key takeaways

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

Reference excerpt

Urocanic acid (formally trans-Urocanic acid) is an intermediate in the catabolism of L-histidine. The cis-urocanic acid isomer is rare.

Ultraviolet radiation absorption Urocanic acid is a chromophore with a strong, broad, and largely structureless absorption band that spans the UV-C and UV-B regions of the electromagnetic spectrum. Experimental measurements consistently find the absorption maximum, λmax, in the range of 267 nm to 280 nm, with the precise value being sensitive to its solvent's pH and polarity.

Metabolism It is formed from L-histidine through the action of histidine ammonialyase (also known as histidase or histidinase) by elimination of ammonium. In the liver, urocanic acid is transformed by urocanate hydratase (or urocanase) to 4-imidazolone-5-propionic acid and subsequently to glutamic acid.

Clinical significance Inherited deficiency of urocanase leads to elevated levels of urocanic acid in the urine, a condition known as urocanic aciduria. An important role for the onset of atopic dermatitis and asthma has been attributed to filaggrin, a skin precursor of urocanic acid. Urocanic acid is thought to be a significant attractant of the nematode parasite Strongyloides stercoralis, in part because of relatively high levels in the plantar surfaces of the feet, the site through which this parasite often enters the body.

Function Urocanic acid is found in animal sweat and skin. its concentration varies greatly between people, from 4 nM per cm2 to 34 nM per cm2 with only small differences between areas other than at the sole of the foot and between sun-exposed and unexposed areas. Concentration does not link with age, sex, skin tone, photosensitivity, and stratum corneum thickness. Among other functions, urocanic acid acts as an endogenous sunscreen or photoprotectant against UVB-induced DNA damage. However, some studies have questioned this. Urocanic acid is found predominantly in the stratum corneum of the skin and it is likely that most of it is derived from filaggrin catabolism (a histidine-rich protein). When exposed to UVB irradiation, trans-urocanic acid is converted in vitro and in vivo to cis-urocanic acid (cis-UCA). The cis form is known to activate regulatory T cells. Measuring cis-UCA provides a sensitive means at sub-erythemal doses to detect UVB, and so offers a potential method to assess the UVR protection provided by suncreams. Some studies attribute filaggrin an important role in keeping the skin surface slightly acidic, through a breaking down mechanism to form histidine and subsequently trans-urocanic acid, however others have shown that the filaggrin–histidine–urocanic acid cascade is not essential for skin acidification.

History Urocanic acid was first isolated in 1874 by the chemist Max Jaffé from the urine of a dog, hence the name (Latin: urina = urine, and canis = dog).

See also Histidinemia Inborn error of metabolism

References

External links The Online Metabolic and Molecular Bases of Inherited Disease - Chapter 80 - An overview of disorders of histidine metabolism, including urocanic aciduria.

Illustrations

Worked examples

Example 1 — a first encounter with Urocanic acid

Start with the simplest possible case. Write down what Urocanic acid 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 Urocanic acid 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 Urocanic acid 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 Urocanic acid

In research: Urocanic acid 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 Urocanic acid 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: Urocanic acid is common in secondary-school and first-year university syllabi. It links to neighbouring topics Alkene derivatives, Carboxylic acids, Imidazoles, so understanding it makes those chapters shorter.
In everyday life: Look for Urocanic acid 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 Urocanic acid in 20 minutes

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

Frequently asked questions

What is Urocanic acid in simple terms?

Urocanic acid (formally trans-Urocanic acid) is an intermediate in the catabolism of L-histidine. The cis-urocanic acid isomer is rare.

Why does Urocanic acid 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 Urocanic acid?

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 Urocanic acid.