biology

Proline dehydrogenase

Proline dehydrogenase 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 Proline dehydrogenase rather than just read about it. In short: In enzymology, proline dehydrogenase (PRODH) (EC 1.5.5.2, formerly EC 1.5.99.8) is an enzyme of the oxidoreductase family, active in the oxidation of L-proline to (S)-1-pyrroline-5-carboxylate during proline catabolism. The end product of this reaction is then further oxidized in a (S)-1-pyrroline-5-carboxylate dehydrogenase (P5CDH)-dependent reaction of the proline metabolism, or spent to produce ornithine, a cruci…

Key takeaways

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Reference excerpt

In enzymology, proline dehydrogenase (PRODH) (EC 1.5.5.2, formerly EC 1.5.99.8) is an enzyme of the oxidoreductase family, active in the oxidation of L-proline to (S)-1-pyrroline-5-carboxylate during proline catabolism. The end product of this reaction is then further oxidized in a (S)-1-pyrroline-5-carboxylate dehydrogenase (P5CDH)-dependent reaction of the proline metabolism, or spent to produce ornithine, a crucial metabolite of ornithine and arginine metabolism. The systematic name of this enzyme class is L-proline:quinone oxidoreductase. Other names in common use include L-proline dehydrogenase, L-proline oxidase, and L-proline:(acceptor) oxidoreductase. It employs one cofactor, flavin adenine dinucleotide (FAD), which requires riboflavin (vitamin B2). Proline dehydrogenase is in humans encoded by PRODH and PRODH2 genes, located on the chromosomes 22 and 19, respectively. Their mutations lead to hyperprolinemia, manifested by increased proline levels in blood and urine. The deficiency of PRODH has also been linked to the susceptibility to schizophrenia-4.

Structure The tertiary structure of PRODH consists of two interacting protein chains, connected by a mutual interaction between alpha helices of both chains. Each protein chain binds a separate FAD cofactor, necessary for the oxidative activity of the enzyme. The binding of FAD is mediated by electrostatic and non-polar interactions between the cofactor and twelve amino acid residues. In some bacteria, PRODH activity is exhibited in combination with the activity of (S)-1-pyrroline-5-carboxylate dehydrogenase (P5CDH) in an enzyme encoded by Proline Utilization A (putA) gene. Despite being two separate enzymes, eukaryote PRODH and P5CDH also show substrate channeling capabilities.

Function PRODH catalyzes the first step of proline catabolism, an FAD-dependent oxidation of proline, summarized by a chemical reaction:

The product, (S)-1-pyrroline-5-carboxylic acid is in chemical equilibrium with L-glutamate-5-semialdehyde. PRODH is located in the inner mitochondrial membrane, which enables the electrons to be transferred to ubiquinone, a final electron acceptor of the reaction. The activity of this enzyme regulates endogenous proline content, all the while providing reducing power to the electron transport chain, eventually producing ATP.

In plants PRODH is crucial in regulating intracellular levels of proline, which is an osmotically active compound important in preventing water losses under abiotic stress. Arabidopsis genome contains two PRODH isoforms, PRODH1 and PRODH2, the latter active in response to the osmotic and biotic stress. Since the electrons abstracted from L-proline are transferred to electron transport chain, an excessive activity of PRODH may overload the electron transport chain, leading to the generation of reactive oxygen species (ROS), contributing to the hypersensitive response during biotic stress.

Structural studies As of late 2007, 9 structures have been solved for this class of enzymes, with PDB accession codes PDB: 1K87, PDB: 1TIW, PDB: 1TJ0, PDB: 1TJ1, PDB: 1TJ2, PDB: 1Y56, PDB: 2FZM, PDB: 2FZN, and PDB: 2G37.

References

Illustrations

Worked examples

Example 1 — a first encounter with Proline dehydrogenase

Start with the simplest possible case. Write down what Proline dehydrogenase 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 Proline dehydrogenase 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 Proline dehydrogenase 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 Proline dehydrogenase

In research: Proline dehydrogenase 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 Proline dehydrogenase 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: Proline dehydrogenase is common in secondary-school and first-year university syllabi. It links to neighbouring topics EC 1.5.5, Enzymes of known structure, Flavoproteins, so understanding it makes those chapters shorter.
In everyday life: Look for Proline dehydrogenase 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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Frequently asked questions

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Why does Proline dehydrogenase 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.

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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.

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