biology

Phosphofructokinase

Phosphofructokinase 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 Phosphofructokinase rather than just read about it. In short: Phosphofructokinase (PFK) is a kinase enzyme that phosphorylates fructose 6-phosphate in glycolysis. Function The enzyme-catalysed transfer of a phosphoryl group from ATP is an important reaction in a wide variety of biological processes.

Key takeaways

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

Reference excerpt

Phosphofructokinase (PFK) is a kinase enzyme that phosphorylates fructose 6-phosphate in glycolysis.

Function The enzyme-catalysed transfer of a phosphoryl group from ATP is an important reaction in a wide variety of biological processes. Phosphofructokinase catalyses the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate, a key regulatory step in the glycolytic pathway. It is allosterically inhibited by ATP and allosterically activated by AMP, thus indicating the cell's energetic needs when it undergoes the glycolytic pathway. PFK exists as a homotetramer in bacteria and mammals (where each monomer possesses 2 similar domains) and as an octomer in yeast (where there are 4 alpha- (PFK1) and 4 beta-chains (PFK2), the latter, like the mammalian monomers, possessing 2 similar domains). This protein may use the morpheein model of allosteric regulation. PFK is about 300 amino acids in length, and structural studies of the bacterial enzyme have shown it comprises two similar (alpha/beta) lobes: one involved in ATP binding and the other housing both the substrate-binding site and the allosteric site (a regulatory binding site distinct from the active site, but that affects enzyme activity). The identical tetramer subunits adopt 2 different conformations: in a 'closed' state, the bound magnesium ion bridges the phosphoryl groups of the enzyme products (ADP and fructose-1,6-bisphosphate); and in an 'open' state, the magnesium ion binds only the ADP, as the 2 products are now further apart. These conformations are thought to be successive stages of a reaction pathway that requires subunit closure to bring the 2 molecules sufficiently close to react. The reverse reaction is catalyzed by the enzyme Fructose-1,6-bisphosphatase.

Phosphofructokinase family PFK belongs to the phosphofructokinase B (PfkB) family of sugar kinases. Other members of this family (also known as the Ribokinase family) include ribokinase (RK), adenosine kinase (AK), inosine kinase, and 1-phosphofructokinase. The members of the PfkB/RK family are identified by the presence of three conserved sequence motifs. The structures of several PfK family of proteins have been determined from a number of organisms and the enzymatic activity of this family of protein shows a dependence on the presence of pentavalent ions. PFK is found in isoform versions in skeletal muscle (PFKM), in the liver (PFKL), and from platelets (PFKP), allowing for tissue-specific expression and function. It is still speculated that the isoforms may play a role in specific glycolytic rates in the tissue-specific environments they are in. It has been found in humans that some human tumor cell lines had increased glycolytic productivity and correlated with the increased amount of PFKL.

Clinical significance Deficiency in PFK leads to glycogenosis type VII (Tarui's disease), an autosomal recessive disorder characterised by severe nausea, vomiting, muscle cramps and myoglobinuria in response to bursts of intense or vigorous exercise. Sufferers are usually able to lead a reasonably ordinary life by learning to adjust activity levels.

Regulation

There are two different phosphofructokinase enzymes in humans:

See also Phosphofructokinase deficiency (GSD type VII, Tarui's disease)

References

External links Phosphofructokinases at the U.S. National Library of Medicine Medical Subject Headings (MeSH)

Illustrations

Worked examples

Example 1 — a first encounter with Phosphofructokinase

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

In research: Phosphofructokinase 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 Phosphofructokinase 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: Phosphofructokinase is common in secondary-school and first-year university syllabi. It links to neighbouring topics EC 2.7.1, Glycolysis enzymes, Moonlighting proteins, so understanding it makes those chapters shorter.
In everyday life: Look for Phosphofructokinase 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 Phosphofructokinase in 20 minutes

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

Frequently asked questions

What is Phosphofructokinase in simple terms?

Phosphofructokinase (PFK) is a kinase enzyme that phosphorylates fructose 6-phosphate in glycolysis. Function The enzyme-catalysed transfer of a phosphoryl group from ATP is an important reaction in a wide variety of biological processes.

Why does Phosphofructokinase 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 Phosphofructokinase?

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 Phosphofructokinase.