biology

Histidinol dehydrogenase

Histidinol 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 Histidinol dehydrogenase rather than just read about it. In short: In enzymology, histidinol dehydrogenase (HIS4) (HDH) (EC 1.1.1.23) is an enzyme that catalyzes the chemical reaction The two substrates of this enzyme are L-histidinol and oxidised nicotinamide adenine dinucleotide (NAD+). Its products are L-histidine, reduced NADH, and two protons.

Key takeaways

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Reference excerpt

In enzymology, histidinol dehydrogenase (HIS4) (HDH) (EC 1.1.1.23) is an enzyme that catalyzes the chemical reaction

The two substrates of this enzyme are L-histidinol and oxidised nicotinamide adenine dinucleotide (NAD+). Its products are L-histidine, reduced NADH, and two protons. 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 L-histidinol:NAD+ oxidoreductase. This enzyme is also called L-histidinol dehydrogenase.

Structure In bacteria, HDH is a single chain polypeptide; in fungi it is the C-terminal domain of a multifunctional enzyme which catalyses three different steps of histidine biosynthesis; and in plants it is expressed as a nuclear encoded protein precursor which is exported to the chloroplast.

Active site Histidinol is held inside the active site thanks to a zinc ion, but the zinc ion does not participate in the catalysis otherwise. The zinc ion is held in place by His262, Gln259, Asp360 and His419 (which, in homodimeric histidinol dehydrogenases, comes from the other monomer). Histidinol itself is held in place by His327 and His367 from one moment unit and Glu414 from the other monomer unit. A Cys residue has been implicated in the catalytic mechanism of the second oxidative step. However, according to newer studies with histidinol dehydrogenase from E. coli, the mechanism is catalyzed by four bases, B1-B4. His327 acts as the first base, deprotonating histidinol's hydroxyl group. Concomitantly, hydride is abstracted from histidinol by NAD+, which is then exchanged for a second NAD+ molecule. Glu325 acts as the second base, deprotonating a molecule of water, which then attacks histidinol. At the same time, His327 (now protonated) donates a proton to the aldehydic oxygen, which results in a gem-diol. After then, His327 again deprotonates one of the hydroxyl groups and NAD+ abstracts a proton from the reactive carbon atom. This series of steps oxidizes the hydroxyl group to a carboxylic acid.

Function Histidinol dehydrogenase catalyzes the terminal step in the biosynthesis of histidine in bacteria, fungi, and plants, the four-electron oxidation of L-histidinol to histidine. In 4-electron dehydrogenases, a single active site catalyses 2 separate oxidation steps: oxidation of the substrate alcohol to an intermediate aldehyde; and oxidation of the aldehyde to the product acid, in this case His. The reaction proceeds via a tightly- or covalently-bound intermediate, and requires the presence of 2 NAD molecules. By contrast with most dehydrogenases, the substrate is bound before the NAD coenzyme.

Co-regulation of the gene Histodinol dehydrogenase gene (HIS4) has been shown co-regulating the adjacent gene while it is under amino acids selective pressure.

Structural studies As of late 2007, 4 structures have been solved for this class of enzymes, with PDB accession codes PDB: 1K75, PDB: 1KAE, PDB: 1KAH, and PDB: 1KAR.

References

Further reading Adams E (1954). "Enzymatic synthesis of histidine from histidinol". J. Biol. Chem. 209 (2): 829–846. doi:10.1016/S0021-9258(18)65512-7. PMID 13192138. Adams E (1955). "L-Histidinal, a biosynthetic precursor of histidine". J. Biol. Chem. 217 (1): 325–344. doi:10.1016/S0021-9258(19)57184-8. PMID 13271397. Yourno J, Ino I (1968). "Purification and crystallization of histidinol dehydrogenase from Salmonella typhimurium LT-2". J. Biol. Chem. 243 (12): 3273–6. doi:10.1016/S0021-9258(18)93303-X. PMID 4872177. Loper JC (1968). "Histidinol dehydrogenase from Salmonella typhimurium Crystallization and composition studies". J. Biol. Chem. 243 (12): 3264–72. doi:10.1016/S0021-9258(18)93302-8. PMID 4872176.

Illustrations

Worked examples

Example 1 — a first encounter with Histidinol dehydrogenase

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

In research: Histidinol 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 Histidinol 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: Histidinol dehydrogenase is common in secondary-school and first-year university syllabi. It links to neighbouring topics EC 1.1.1, EC 1.1.1 stubs, Enzymes of known structure, so understanding it makes those chapters shorter.
In everyday life: Look for Histidinol 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

What is Histidinol dehydrogenase in simple terms?

In enzymology, histidinol dehydrogenase (HIS4) (HDH) (EC 1.1.1.23) is an enzyme that catalyzes the chemical reaction The two substrates of this enzyme are L-histidinol and oxidised nicotinamide adenine dinucleotide (NAD+). Its products are L-histidine, reduced NADH, and two protons.

Why does Histidinol 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.

How should I study Histidinol 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 Histidinol dehydrogenase.