chemistry

Pinnatoxin

Pinnatoxin 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 Pinnatoxin rather than just read about it. In short: Pinnatoxins are paralytic chemical compounds that inhibit neuronal and muscle-type nicotinic acetylcholine receptors. Although first discovered in shellfish, they are produced by the Peridiniacean dinoflagellate Vulcanodinium rugosum.

Key takeaways

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

Reference excerpt

Pinnatoxins are paralytic chemical compounds that inhibit neuronal and muscle-type nicotinic acetylcholine receptors. Although first discovered in shellfish, they are produced by the Peridiniacean dinoflagellate Vulcanodinium rugosum. Eight subtypes, designated pinnatoxin A-H, have been described.

Discovery and distribution Pinnatoxins are neurotoxins named after the genus Pinna, a group of bivalve molluscs, in reference to their original isolation from members of the genus Pinna attenuata and later Pinna muricata. The causative organism producing the toxin was later identified as the dinoflagellate Vulcanodinium rugosum. The presence of the toxin has been identified in various locations, including the Pacific Ocean, the Persian Gulf, the Mediterranean Sea, waters near Canada, Scandinavia, and South China, and in water samples in Ireland.

Chemistry Pinnatoxins are part of the cyclic imine group of marine toxins. This group currently consists of pinnatoxins, pteriatoxins, spirolides, gymnodimines, spiro-prorocentimine and portimine. Eight different types of pinnatoxins have been described, named pinnatoxin A to H. All the pinnatoxins contain several key structural elements. The structure of pinnatoxin is composed of a cyclic imine (A ring) spirolinked to a cyclohexene ring (G ring), a dispiro 6,5,6 tricyclic ketal at C12-C23 (rings B, C, D), a bridged bicyclic ketal at C25-C30 (rings E, F) and a 27-membered macrocyclic ring spanning C5-C31.

Table: molecular formula and molecular weight of pinnatoxins

Target Pinnatoxin A, G, E and F display a high-affinity antagonism for the neuronal α7 and muscle α12βϒδ nicotine acetylcholine receptors (nAChRs). The affinity of pinnatoxins for nAChR subtypes is the result of a selectivity mechanism: the bulky bridged EF-ketal ring, specific for pinnatoxins, is able to interact with the sequence-variable loop F of the nAChRs. The inhibitory potency of pinnatoxin A depends on the nAChR subtype. It has the following ranking in selectivity: α7> α12βϒδ>α4β2. Pinnatoxin A has a 300-fold greater potency toward the α7 than to the α4β2 nAChR. Furthermore, the blocking of α7 appears to be irreversible. Pinnatoxin G shows no selectivity between the two neuronal subtypes α7 en α4β2 nAChRs. In contrast, pinnatoxin G interacts with 25-fold higher affinity than pinnatoxin A on the muscle-type nAChR. So the selectivity rank ordering of pinnatoxin G is α12βϒδ> α7 > α3β2 α4β2. Pinnatoxin E and F have the same order of selectivity for these receptors, although they differ in their potency. The rank order of potency at all receptors is F>G>E.

Mode of action Pinnatoxins are potent inhibitors of neuronal and muscle type nicotine acetylcholine receptors (nAChRs). They block the nAChR through adherence to the receptor binding site. Different subregions of the pinnatoxin molecule have multiple anchoring points in the receptor-binding site, through which they dictate the tight binding between the opposing loops C and F at the nAChR subunit interface. When pinnatoxin G and F are bound to the nAChR, they can both reduce or even abolish the amplitude of miniature endplate potentials and nerve-evoked endplate potentials. They do not have an effect on the firing frequency or resting membrane potential. This is characteristic of a postsynaptic mechanism of action.

Toxicity As of today, no pinnatoxin or cyclic imine has been linked to human poisoning. The toxic effects of pinnatoxin E-H have, however, been examined on female Swiss albino mice. The symptoms exhibited by mice exposed to a lethal dose of pinnatoxin by intraperitoneal injection are very similar between pinnatoxin E, F, G and H. The symptoms start off with a period of hyperactivity until 10–20 minutes after injection, when an abrupt decrease in activity occurs. In the case of pinnatoxin H injection, mice become immobile instead of hyperactive. During this decrease in activity/occurrence of immobility, abdominal breathing and extension of the hind legs are observed. In some cases, mice suffer from slight exophthalmia. After this period, during which the respiration rate remains normal, the respiration rate declines rapidly within a 2 to 3-minute time interval. Death is preceded by a brief period of running movements, the occurrence of cyanosis and severe exophthalmos. The time between dosing and death varies between 14 and 50 minutes. Apart from the greater time to onset of inactivity and abdominal breathing at lethal doses (25–40 minutes), and the time to death (approximately 1.3 hours), the symptoms after pinnatoxin E, F or G admission by gavage do not differ much from admission by intraperitoneal injection. In contrast, the time to death after admission of pinnatoxin H by intraperitoneal injection or gavage did not differ. The behavioural abnormalities observed in mice after a sublethal dose start off with a hyperactive or immobile period shortly after toxin admission, and end with a full recovery. Furthermore, none of the toxins described above lead to aberrant behaviour or abnormal appearance during a subsequent 14-day observation period, nor do they result in any atypical observations at necropsy. However, the symptoms after the hyperactive/immobile period until full recovery, differ between the pinnatoxins:

After pinnatoxin E dosing, mice become very lethargic, achieving full recovery within an hour. A sublethal pinnatoxin F dosing results in immobility, without full recovery until 2–3 hours after toxin admission. A sublethal pinnatoxin H dosing results in immobility as well, with full recovery after an unspecified time span. 9–13 minutes after pinnatoxin G admission, mice become very lethargic and show an abdominal breathing pattern, while the respiration rate remains normal. Full recovery occurs within 2 hours.

References

Illustrations

Worked examples

Example 1 — a first encounter with Pinnatoxin

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

In research: Pinnatoxin 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 Pinnatoxin 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: Pinnatoxin is common in secondary-school and first-year university syllabi. It links to neighbouring topics Azepines, Cyclohexenes, Invertebrate toxins, so understanding it makes those chapters shorter.
In everyday life: Look for Pinnatoxin 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 Pinnatoxin in 20 minutes

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

Frequently asked questions

What is Pinnatoxin in simple terms?

Why does Pinnatoxin 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 Pinnatoxin?

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 Pinnatoxin.