biology

Histidine ammonia-lyase

Histidine ammonia-lyase is a biology 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 Histidine ammonia-lyase rather than just read about it. In short: Histidine ammonia-lyase (EC 4.3.1.3, histidase, histidinase) is an enzyme that in humans is encoded by the HAL gene. It converts histidine into ammonia and urocanic acid.

Key takeaways

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

Reference excerpt

Histidine ammonia-lyase (EC 4.3.1.3, histidase, histidinase) is an enzyme that in humans is encoded by the HAL gene. It converts histidine into ammonia and urocanic acid. Its systematic name is L-histidine ammonia-lyase (urocanate-forming).

Function Histidine ammonia-lyase is a cytosolic enzyme catalyzing the first reaction in histidine catabolism, the nonoxidative deamination of L-histidine to trans-urocanic acid. The reaction is catalyzed by 3,5-dihydro-5-methyldiene-4H-imidazol-4-one (MIO), an electrophilic cofactor which is formed autocatalytically by cyclization of the protein backbone of the enzyme.

Pathology Mutations in the gene for histidase are associated with histidinemia and urocanic aciduria.

See also Phenylalanine ammonia-lyase, another enzyme that contains the MIO cofactor

References

Illustrations

Worked examples

Example 1 — a first encounter with Histidine ammonia-lyase

Start with the simplest possible case. Write down what Histidine ammonia-lyase claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, 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 Histidine ammonia-lyase 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 Histidine ammonia-lyase 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 Histidine ammonia-lyase

In research: Histidine ammonia-lyase appears in biology 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 Histidine ammonia-lyase 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: Histidine ammonia-lyase is common in secondary-school and first-year university syllabi. It links to neighbouring topics EC 4.3.1, Genes on human chromosome 12, Lyase stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Histidine ammonia-lyase 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 Histidine ammonia-lyase in 20 minutes

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

Frequently asked questions

What is Histidine ammonia-lyase in simple terms?

Histidine ammonia-lyase (EC 4.3.1.3, histidase, histidinase) is an enzyme that in humans is encoded by the HAL gene. It converts histidine into ammonia and urocanic acid.

Why does Histidine ammonia-lyase matter?

Because it connects several biology 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 Histidine ammonia-lyase?

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 Histidine ammonia-lyase.