biology

Proctolin

Proctolin 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 Proctolin rather than just read about it. In short: Proctolin is a neuropeptide present in insects and crustaceans. It was first found in Periplaneta americana, a species of cockroach in 1975.

Key takeaways

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

Reference excerpt

Proctolin is a neuropeptide present in insects and crustaceans. It was first found in Periplaneta americana, a species of cockroach in 1975. Proctolin was extracted from 125,000 cockroaches and the Edman degradation was carried out on the sample to determine the amino acid sequence, which is Arg-Tyr-Leu-Pro-Thr. Proctolin was the first insect neuropeptide to be sequenced. Starratt and Brown identified it as a visceral muscle neurotransmitter. However, it now appears that there are many more functions of proctolin, and it is present in many more species.

Localisation Proctolin is found in the following insect orders:

Orthoptera Hemiptera Diptera Coleoptera Proctolin may also be present in molluscs, annelids, decapod crustaceans, and possibly even some mammals.

Structure The proctolin structure is very highly conserved between species. Proctolin analogs have been synthesised in order to find out more about the structure of the molecule. It was found that each amino acid in the proctolin molecule was needed for full activity. The preferred conformation of proctolin is a quasi-cyclic structure with the tyrosyl side chain pointing outwards. This is the best position for it to bind to the active site of the receptor. A large range of proctolin peptide and nonpeptide mimetics have been synthesised to try and produce new effective insecticides.

Function Proctolin is not considered a classical neurotransmitter as in many systems where it is present it does not change the postsynaptic conductance. It is believed proctolin is a neurohormone in crustaceans and in some insects. More frequently, proctolin is referred to as a neuromodulator. This is because all proctolinergic systems change the way impulses are transmitted across a synapse, using proctolin as a cotransmitter, often with a more common neurotransmitter such as glutamate. Proctolin is a potent stimulator in the contraction of a number of visceral and skeletal muscles in insects. Proctolin stimulates contractions of the hindgut in P. americana, the foregut in S. gregaria and the midgut of Diploptera punctata and L. migratoria. Proctolin also modulates reproductive tissue, stimulating contractions of the oviducts in P. americana, Leucophaea maderae, L. migratoria, and spermathecae in L. migratoria and Rhodnius prolixus. Another function of proctolin is that it speeds up heart rate in some insects. A proctolin receptor in Drosophila melanogaster has been recently identified as the orphan G-protein coupled receptor CG6986. The DNA of the gene sequence was cloned and expressed in mammalian cells and the expressed receptor was specific for proctolin. In Drosophila, this receptor is strongly expressed in the head, the larval hindgut, the aorta and on neuronal endings in adult hearts.

Synthesis and breakdown Through analysis of the Drosophila melanogaster genome, the gene that codes for the proctolin precursor has been identified as CG7105. The pre-proprotein is 140 amino acids long and has cleavage sites either side of the RYLPT proctolin sequence. It is thought a signal peptidase cuts at these cleavage sites to produce the proctolin peptide. Proctolin needs to be broken down to stop it staying permanently bound to the receptor. This is done by peptidases. The first step of breakdown is cleavage of the Arg-Tyr bond, followed by the cleavage of the Tyr-Leu bond. Using a number of tissue homogenates from Periplaneta americana a soluble aminopeptidase as a key enzyme that degrades proctolin was identified. Another enzyme was also identified that cleaves the Tyr-Leu bond.

References

Kastin, Abba J. (2006). Handbook of Biologically Active Peptides. Boston: Academic Press. ISBN 0-12-369442-6. Orchard I, Belanger JH, Lange AB (1989). "Proctolin: a review with emphasis on insects". J. Neurobiol. 20 (5): 470–96. doi:10.1002/neu.480200515. PMID 2568390.

Illustrations

Worked examples

Example 1 — a first encounter with Proctolin

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

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

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

Frequently asked questions

What is Proctolin in simple terms?

Proctolin is a neuropeptide present in insects and crustaceans. It was first found in Periplaneta americana, a species of cockroach in 1975.

Why does Proctolin 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 Proctolin?

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 Proctolin.