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Retinol dehydrogenase

Retinol dehydrogenase is a engineering 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 Retinol dehydrogenase rather than just read about it. In short: In enzymology, retinol dehydrogenase (RDH) (EC 1.1.1.105) is an enzyme that catalyzes the chemical reaction: Sometimes, in addition to or along with NAD+, NADP+ can act as an alternative cofactor in the reaction. The substrate of the enzyme can be all-trans- or -cis- retinol.

Retinol dehydrogenase — main illustration
Retinol dehydrogenase — illustration

Key takeaways

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

Reference excerpt

In enzymology, retinol dehydrogenase (RDH) (EC 1.1.1.105) is an enzyme that catalyzes the chemical reaction:

Sometimes, in addition to or along with NAD+, NADP+ can act as an alternative cofactor in the reaction. The substrate of the enzyme can be all-trans- or -cis- retinol. Some 20 enzymes with RDH activity had been found and studied by 2006. The two substrates of this enzyme are retinol and oxidised nicotinamide adenine dinucleotide (NAD+). Its products are retinal, reduced NADH, and a proton. This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-OH group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is retinol:NAD+ oxidoreductase. Other names in common use include retinol (vitamin A1) dehydrogenase, MDR, microsomal retinol dehydrogenase, all-trans retinol dehydrogenase, retinal reductase, and retinene reductase. This enzyme participates in retinol metabolism. Occasionally, the literature refers to retinol dehydrogenase as an enzyme that oxidizes retinol in general, such as class IV alcohol dehydrogenase (ADH4), which reportedly is the most efficient retinol oxidation in the human alcohol dehydrogenase (ADH) family.

Structure

As one of the most important RDH, 11-cis-retinol dehydrogenase catalyzes the 11-cis retinaldehyde (the most common visual pigments in higher animals) formation. The enzyme is mainly expressed in the retinal pigment epithelium (RPE) and is part of short-chain dehydrogenase (SDR) / reductase superfamily. The integral membrane enzyme is anchored to the membranes by its two hydrophobic chains. The catalytic domain of 11-cis-retinol dehydrogenase is restricted to the lumenal compartment, suggesting its origin from compartmentalized process. 11-cis-retinol dehydrogenase is also mainly associated to the smooth endoplasmic reticulum of RPE cells. The 32-kDa integral membrane protein protein (p32) was found to act as the stereospecific 11-cis-retinol dehydrogenase in the presence of NAD+ cofactor, and p32 catalyzes the biosynthesis of 11-cis retinal commonly found visual chromophore. One of the widely studied genes of retinol dehydrogenase RDH12, which encodes retinol dehydrogenase is part of the superfamily of short-chained alcohol dehydrogenases and reductases. RDH12 is mainly expressed in neuroretina and is composed of 7 exons encoding a 360-amino acid peptide. Zinc molecules serve as the ligand cofactor with the cofactor NAD. The retinol will interact with the enzyme at the area between those two cofactors. However, not all retinol dehydrogenases in visual cycle are identified, and this remains challenging to scientists due to the overlapping expressions and activity redundancy among two large RDH and RDH-like producing classes: microsomal short-chain dehydrogenase/reductase and cytosolic medium-chain alcohol dehydrogenases. In Bovine, retinol dehydrogenase is found as a part of retinal rod outer segments and shows difficulty when separating from membrane. Its Stokes radius is 8.5 nm in Lubrol 12A9 mixed micelle.

Function Retinoid dehydrogenases/reductases (oxidoreductases), including retinol dehydrogenase, catalyze the key oxidation-reduction reactions in the visual cycle, converting vitamin A to 11-cis retinal, which is the chromophore of the rod and cone photoreceptors. It is believed that RDHs at rod and cone are different, but related and can catalyze the same reaction. RDH12 is the primary enzyme that reduces all-trans retinal released from bleached photopigments during recovery phase in the visual cycle. The RDH12 enzyme can use either cis or trans retinoid isomers as substrates and can also function as both dehydrogenase (i.e. retinol to retinal) and reductase (i.e. retinal to retinol). The conversion of retinol to retinal is the rate-limiting step in the retinoic acid biosynthesis. In vertebrates, the retinoic acid is the ligand that controls nuclear receptor signaling pathway, which is responsible for growth and development as well as epithelial maintenance, therefore can be used for cancer and acne treatment. In human, ADH4 can exhibit at least 10 folds higher Vmax/Km than other ADH.

Some retinol dehydrogenases are in extra-ocular tissues, such as human retinol dehydrogenase-4 (RoDH-4), which converts retinol and 1-cis-retinol to different aldehydes in liver and skin. It was also found that 13-cis-retinoic acid (isotretinoin), 3,4-didehydroretinoic acid, and 3,4-didehydroretinol can act as competitive inhibitor of the 3α-hydroxysteroid dehydrogenase oxidative activity of the enzyme. This can potentially explain how isotretinoin, the active ingredient is Roaccutane (Accutane), can suppress sebaceous glands and be used for severe acne treatment.

Disease relevance The missense mutation in gene rdh5, which codes for microsomal 11-cis-retinol dehydrogenase (RDH5), causes fundus albipunctatus, whose symptoms include retinal white-spot accumulation, stationary night blindness caused by delay in cone and rod photopigment regeneration, and elderly cone dystrophy. At least 20 mutations in rdh12 gene, which encodes retinol dehydrogenase, can be associated to diseases, including severe and early-onset autosomal recessive retinal dystrophy (arRD), or Leber congenital amaurosis. Patients suffer from cone and rod malfunction since childhood and develop legal blindness when reaching adulthood. This suggests that RDH12 might play a central role in the visual cycle and can be a promising therapeutic target. A possible mechanism of the accelerated degradation among RDH12 mutants is the polyubiquitination by cytosolic ubiquitin ligases and subsequent degradation by proteosome. Its conformation aberration provokes the aforementioned accelerated degradation.

References

Illustrations

Retinol dehydrogenase illustration
Retinol dehydrogenase: Image 1: Wild-type human sigma (class IV) alcohol dehydrogenase (1D1S) has retinol dehydrogenase activity. Zinc molecules are depicted as red balls, while NAD molecules are purple. Note that the enzyme exists as two protein units in this figure. (PDB file from RCSB)[6]
Image 1: Wild-type human sigma (class IV) alcohol dehydrogenase (1D1S) has retinol dehydrogenase activity. Zinc molecules are depicted as red balls, while NAD molecules are purple. Note that the enzyme exists as two protein units in this figure. (PDB file from RCSB)[6]
Retinol dehydrogenase: Image 2: Wild-type human sigma (class IV) alcohol dehydrogenase (1D1S). Retinols will bind between the catalytic zinc molecules (red balls) and the NAD molecule (purple).[7] (PDB file from RCSB)[6]
Image 2: Wild-type human sigma (class IV) alcohol dehydrogenase (1D1S). Retinols will bind between the catalytic zinc molecules (red balls) and the NAD molecule (purple).[7] (PDB file from RCSB)[6]
Retinol dehydrogenase: Image 3: The visual phototransduction cycle yields 11-cis-retinal from 11-cis-retinol using 11-cis-retinol dehydrogenase.[11][13][15]
Image 3: The visual phototransduction cycle yields 11-cis-retinal from 11-cis-retinol using 11-cis-retinol dehydrogenase.[11][13][15]

Worked examples

Example 1 — a first encounter with Retinol dehydrogenase

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

In research
Retinol dehydrogenase appears in engineering 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 Retinol 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
Retinol dehydrogenase is common in secondary-school and first-year university syllabi. It links to neighbouring topics EC 1.1.1, Enzymes of unknown structure, NADH-dependent enzymes, so understanding it makes those chapters shorter.
In everyday life
Look for Retinol 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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How to study Retinol dehydrogenase in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Retinol dehydrogenase means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Retinol dehydrogenase out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Retinol dehydrogenase in simple terms?

In enzymology, retinol dehydrogenase (RDH) (EC 1.1.1.105) is an enzyme that catalyzes the chemical reaction: Sometimes, in addition to or along with NAD+, NADP+ can act as an alternative cofactor in the reaction. The substrate of the enzyme can be all-trans- or -cis- retinol.

Why does Retinol dehydrogenase matter?

Because it connects several engineering 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 Retinol dehydrogenase?

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 Retinol dehydrogenase.

Tags

  • EC 1.1.1
  • Enzymes of unknown structure
  • NADH-dependent enzymes

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