science

PYGB

PYGB is a science 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 PYGB rather than just read about it. In short: Glycogen phosphorylase, brain (PYGB, GPBB), is an enzyme that in humans is encoded by the PYGB gene on chromosome 20. The protein encoded by this gene is a glycogen phosphorylase found predominantly in the brain.

Key takeaways

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

Reference excerpt

Glycogen phosphorylase, brain (PYGB, GPBB), is an enzyme that in humans is encoded by the PYGB gene on chromosome 20. The protein encoded by this gene is a glycogen phosphorylase found predominantly in the brain. The encoded protein forms homodimers, which can associate into homotetramers, the enzymatically active form of glycogen phosphorylase. The activity of this enzyme is positively regulated by AMP and negatively regulated by ATP, ADP, and glucose-6-phosphate. This enzyme catalyzes the rate-determining step in glycogen degradation. [provided by RefSeq, Jul 2008]

Structure The PYGB gene encodes one of three major glycogen phosphorylase isoforms, which are distinguished by their different structures and subcellular localizations: brain (PYGB), muscle (PYGM), and liver (PYGL). GPBB is the longest of the three isozymes, with a length of 862 residues, due to the extended 3'-UTR at the enzyme's C-terminal. Nonetheless, it shares high homology in amino acid sequence with the other two isozymes, with 83% similarity with PYGM and 80% similarity with PYGL. Moreover, both its nucleotide and amino acid sequences and its codon usage share higher similarity with those of PYGM, thus indicating that the two share a closer evolutionary descent by gene duplication and translocation of a common ancestral gene. A possible pseudogene can be found on chromosome 10.

Function As a glycogen phosphorylase, GPBB catalyzes the phosphorolysis of glycogen to yield glucose 1-phosphate. This reaction serves as the rate-determining first step in glycogenolysis and, thus, contributes to the regulation of carbohydrate metabolism. In particular, GPBB is responsible for supplying emergency glucose during periods of stress, including anoxia, hypoglycemia, or ischemia. In normal cell conditions, GPBB is bound to the sarcoplasmic reticulum (SR) membrane by complexing with glycogen. When stimulated by stress conditions, Under stress conditions such as hypoxia, glycogen is degraded, and GPBB is released into the cytoplasm. Though GPBB is primarily expressed in adult and fetal brain, it has also been detected in cardiomyocytes and at low levels in other adult and fetal tissues. These other tissues also express PYGL and PYGM, but the purpose of expressing multiple glycogen phosphorylases remains unclear. Nuclear localization was also cited for GPBB in gastrointestinal cancer.

Clinical significance

Cancer GPBB overexpression has been associated with several cancers, including colorectal cancer, gastrointestinal cancer, and non-small cell lung cancer (NSCLC). Since GPBB is upregulated during the potential transition of adenoma cells into carcinoma cells, GPBB may be a useful biomarker to detect malignancy potential in precancerous lesions.

Ischemia Since GPBB is released from the SR membrane under ischemic conditions, it may serve as a biomarker for early detection of ischemia. Specifically, its release in acute myocardial ischemia has been attributed to increased glycogenolysis and plasma membrane permeability, and has been correlated with poor outcome. As a highly sensitive marker for myocardial ischemia, GPBB may aid in the detection of perioperative myocardial damage and infarction in patients undergoing coronary artery bypass grafting. Meanwhile, GPBB levels are elevated in patients with hypertrophic cardiomyopathy.

Worked examples

Example 1 — a first encounter with PYGB

Start with the simplest possible case. Write down what PYGB claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 PYGB 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 PYGB 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 PYGB

In research: PYGB appears in science 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 PYGB 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: PYGB is common in secondary-school and first-year university syllabi. It links to neighbouring topics Enzymes, so understanding it makes those chapters shorter.
In everyday life: Look for PYGB 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 “PYGB” →

Affiliate

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

How to study PYGB in 20 minutes

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

Frequently asked questions

What is PYGB in simple terms?

Why does PYGB matter?

Because it connects several science 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 PYGB?

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 PYGB.