Peptide YY

Key takeaways

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

Reference excerpt

Peptide YY (PYY), also known as peptide tyrosine tyrosine, is a peptide that in humans is encoded by the PYY gene. Peptide YY is a short (36-amino acid) peptide released from cells in the ileum and colon in response to feeding. In the blood, gut, and other elements of periphery, PYY acts to reduce appetite; similarly, when injected directly into the central nervous system, PYY is also anorexigenic, i.e., it reduces appetite. Dietary fibers from fruits, vegetables, and whole grains, consumed, increase the speed of transit of intestinal chyme into the ileum, to raise PYY3-36, and induce satiety. Peptide YY cannot be produced as the result of enzymatic breakdown of crude fish proteins and ingested as a food product.

Structure Peptide YY is related to the pancreatic peptide family by having 18 of its 36 amino acids located in the same positions as pancreatic peptide. The two major forms of peptide YY are PYY1-36 and PYY3-36, which have PP fold structural motifs. However, the most common form of circulating PYY immunoreactivity is PYY3-36, which binds to the Y2 receptor (Y2R) of the Y family of receptors. Peptide YY3-36 (PYY) is a linear polypeptide consisting of 36 amino acids with structural homology to NPY and pancreatic polypeptide. The PP-fold motif is found throughout this family and relates to the 3D structure. The PP-fold is formed through the incorporation of certain residues which are predominately Pro2, Pro5, Pro8, Gly9, Tyr20 and Tyr27. This PP-fold has been found to protect the peptide against enzymatic attack as well as producing a hydrophobic pocket which is inherently overall energy reducing. In addition to containing the PP-fold motif, PYY and its derivative PYY3- 36 also have a high C-terminal α-helix proportion, suggested to be extremely important for the structural integrity of PYY.

Release PYY is found in L cells in the mucosa of gastrointestinal tract, especially in ileum and colon. Also, a small amount of PYY, about 1-10%, is found in the esophagus, stomach, duodenum and jejunum. PYY concentration in the circulation increases postprandially (after food ingestion) and decreases by fasting. In addition, PYY is produced by a discrete population of neurons in the brainstem, specifically localized to the gigantocellular reticular nucleus of the medulla oblongata. C. R. Gustavsen et al. had found PYY-producing cells located in the islets of Langerhans in rats. They were observed either alone or co-localized with glucagon or PP. PYY is released by the L-cells of the gastrointestinal tract following food intake, and there are two main endogenous forms: PYY1-36 and PYY3-36. PYY1-36 is rapidly processed by the enzyme DPP4 to the 34-amino acid peptide PYY3-36. DPP4 hydrolyses PYY and removes the first two amino acids, tyrosine and proline, at the N-terminal, which changes the receptor selectivity. As a result of this, PYY3-36 has a high selectivity for the Y2-receptor, compared to PYY1-36 which has selectivity for the Y1, Y2, and Y5 receptors. It is thought that the Y1 receptor requires both the C-terminus and N-terminus for recognition, binding and then subsequent activation. The Y2 receptor is thought to have a smaller receptor site and also only requires the C-terminus for recognition. This could explain the reduced affinity for PYY3-36 on any other Y receptor other than Y2. Other studies replacing the amide bonds with ester bonds also confirm that the end section is important in binding and activation. The Y2 receptors are located in the hippocampus, sympathetic and parasympathetic nerve fibres, intestines, and certain blood vessels, and have been implicated in regulating food intake and gastric emptying. As a result of this, the Y2 receptor is considered a target for the treatment of obesity and type II diabetes.

Function PYY exerts its action through NPY receptors; it inhibits gastric motility and increases water and electrolyte absorption in the colon. PYY may also suppress pancreatic secretion. It is secreted by the neuroendocrine cells in the ileum and colon in response to a meal, and has been shown to reduce appetite. PYY works by slowing the gastric emptying; hence, it increases efficiency of digestion and nutrient absorption after a meal. Research has also indicated PYY may be useful in removing aluminium accumulated in the brain.

Animal studies Several studies have shown acute peripheral administration of PYY3-36 inhibits feeding of rodents and primates. Other studies on Y2R-knockout mice have shown no anorectic effect on them. These findings indicate PYY3-36 has an anorectic (losing appetite) effect, which is suggested to be mediated by Y2R. PYY-knockout female mice increase in body weight and fat mass. PYY-knockout mice, on the other hand, are resistant to obesity, but have higher fat mass and lower glucose tolerance when fed a high-fat diet, compared to control mice. Thus, PYY also plays a very important role in energy homeostasis by balancing food intake. PYY oral spray was found to promote fullness. Viral gene therapy of the salivary glands resulted in long-term intake reduction.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Peptide YY

Start with the simplest possible case. Write down what Peptide YY 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 Peptide YY 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 Peptide YY 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 Peptide YY

In research: Peptide YY 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 Peptide YY 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: Peptide YY is common in secondary-school and first-year university syllabi. It links to neighbouring topics Genes on human chromosome 17, Nutrition, Obesity, so understanding it makes those chapters shorter.
In everyday life: Look for Peptide YY 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.

How to study Peptide YY in 20 minutes

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

Frequently asked questions

What is Peptide YY in simple terms?

Peptide YY (PYY), also known as peptide tyrosine tyrosine, is a peptide that in humans is encoded by the PYY gene. Peptide YY is a short (36-amino acid) peptide released from cells in the ileum and colon in response to feeding.

Why does Peptide YY 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 Peptide YY?

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 Peptide YY.