chemistry

Isoleucine

Isoleucine 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 Isoleucine rather than just read about it. In short: Isoleucine (symbol Ile or I) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH+3 form under biological conditions), an α-carboxylic acid group (which is in the deprotonated −COO− form under biological conditions), and a hydrocarbon side chain with a branch (a central carbon atom bound to three other carbon atoms).

Key takeaways

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

Reference excerpt

Isoleucine (symbol Ile or I) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH+3 form under biological conditions), an α-carboxylic acid group (which is in the deprotonated −COO− form under biological conditions), and a hydrocarbon side chain with a branch (a central carbon atom bound to three other carbon atoms). It is classified as a non-polar, uncharged (at physiological pH), branched-chain, aliphatic amino acid. It is essential in humans, meaning the body cannot synthesize it. Essential amino acids are necessary in the human diet. In plants isoleucine can be synthesized from threonine and methionine. In plants and bacteria, isoleucine is synthesized from a pyruvate employing leucine biosynthesis enzymes. It is encoded by the codons AUU, AUC, and AUA.

Metabolism

Biosynthesis In plants and microorganisms, isoleucine is synthesized from pyruvate and alpha-ketobutyrate. This pathway is not present in humans. Enzymes involved in this biosynthesis include:

Acetolactate synthase (also known as acetohydroxy acid synthase) Acetohydroxy acid isomeroreductase Dihydroxyacid dehydratase Valine aminotransferase

Catabolism Isoleucine is both a glucogenic and a ketogenic amino acid. After transamination with alpha-ketoglutarate, the carbon skeleton is oxidised and split into propionyl-CoA and acetyl-CoA. Propionyl-CoA is converted into succinyl-CoA, a TCA cycle intermediate which can be converted into oxaloacetate for gluconeogenesis (hence glucogenic). In mammals acetyl-CoA cannot be converted to carbohydrate but can be either fed into the TCA cycle by condensing with oxaloacetate to form citrate or used in the synthesis of ketone bodies (hence ketogenic) or fatty acids.

Metabolic diseases The degradation of isoleucine is impaired in the following metabolic diseases:

Combined malonic and methylmalonic aciduria (CMAMMA) Maple syrup urine disease (MSUD) Methylmalonic acidemia Propionic acidemia

Insulin resistance Isoleucine, like other branched-chain amino acids, is associated with insulin resistance: higher levels of isoleucine are observed in the blood of diabetic mice, rats, and humans. In diet-induced obese and insulin resistant mice, a diet with decreased levels of isoleucine (with or without the other branched-chain amino acids) results in reduced adiposity and improved insulin sensitivity. Reduced dietary levels of isoleucine are required for the beneficial metabolic effects of a low protein diet. In humans, a protein restricted diet lowers blood levels of isoleucine and decreases fasting blood glucose levels. Mice fed a low isoleucine diet are leaner, live longer, and are less frail. In humans, higher dietary levels of isoleucine are associated with greater body mass index.

Functions and requirement The Food and Nutrition Board (FNB) of the U.S. Institute of Medicine has set Recommended Dietary Allowances (RDAs) for essential amino acids in 2002. For adults 19 years and older, 19 mg of isoleucine/kg body weight is required daily. Beside its biological role as a nutrient, isoleucine also participates in regulation of glucose metabolism. Isoleucine is an essential component of many proteins. As an essential amino acid, isoleucine must be ingested or protein production in the cell will be disrupted. Fetal hemoglobin is one of the many proteins that require isoleucine. Isoleucine is present in the gamma chain of fetal hemoglobin and must be present for the protein to form. Genetic diseases can change the consumption requirements of isoleucine. Amino acids cannot be stored in the body. Buildup of excess amino acids will cause a buildup of toxic molecules so, humans have many pathways to degrade each amino acid when the need for protein synthesis has been met. Mutations in isoleucine-degrading enzymes can lead to dangerous buildup of isoleucine and its toxic derivative. One example is maple syrup urine disease (MSUD), a disorder that leaves people unable to breakdown isoleucine, valine, and leucine. People with MSUD manage their disease by a reduced intake of all three of those amino acids alongside drugs that help excrete built-up toxins. Many animals and plants are dietary sources of isoleucine as a component of proteins. Foods that have high amounts of isoleucine include eggs, soy protein, seaweed, turkey, chicken, lamb, cheese, and fish.

Synthesis Routes to isoleucine are numerous. One common multistep procedure starts from 2-bromobutane and diethylmalonate. Synthetic isoleucine was first reported in 1905 by French chemists Bouveault and Locquin.

Discovery German chemist Felix Ehrlich discovered isoleucine while studying the composition of beet-sugar molasses 1903. In 1907 Ehrlich carried out further studies on fibrin, egg albumin, gluten, and beef muscle in 1907. These studies verified the natural composition of isoleucine. Ehrlich published his own synthesis of isoleucine in 1908.

See also Alloisoleucine, the diasteromer of isoleucine Low Isoleucine protein foods

References

External links Isoleucine degradation Isoleucine biosynthesis

Illustrations

Worked examples

Example 1 — a first encounter with Isoleucine

Start with the simplest possible case. Write down what Isoleucine 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 Isoleucine 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 Isoleucine 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 Isoleucine

In research: Isoleucine 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 Isoleucine 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: Isoleucine is common in secondary-school and first-year university syllabi. It links to neighbouring topics Alpha-Amino acids, Branched-chain amino acids, Essential amino acids, so understanding it makes those chapters shorter.
In everyday life: Look for Isoleucine 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 Isoleucine in 20 minutes

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

Frequently asked questions

What is Isoleucine in simple terms?

Why does Isoleucine 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 Isoleucine?

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 Isoleucine.