engineering

Leghemoglobin reductase

Leghemoglobin reductase 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 Leghemoglobin reductase rather than just read about it. In short: In enzymology, a leghemoglobin reductase (EC 1.6.2.6) is an enzyme that catalyzes the chemical reaction NAD(P)H + H+ + 2 ferrileghemoglobin ⇌ {\displaystyle \rightleftharpoons } NAD(P)+ + 2 ferroleghemoglobin In other words, a leghemoglobin (or phytoglobin in general) with a Fe3+ is reduced to one with the ferrous ion, Fe2+. This enzyme belongs to the family of oxidoreductases, specifically those acting on NADH or N…

Key takeaways

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

Reference excerpt

In enzymology, a leghemoglobin reductase (EC 1.6.2.6) is an enzyme that catalyzes the chemical reaction

NAD(P)H + H+ + 2 ferrileghemoglobin ⇌ {\displaystyle \rightleftharpoons } NAD(P)+ + 2 ferroleghemoglobin In other words, a leghemoglobin (or phytoglobin in general) with a Fe3+ is reduced to one with the ferrous ion, Fe2+. This enzyme belongs to the family of oxidoreductases, specifically those acting on NADH or NADPH with a heme protein as acceptor. The systematic name of this enzyme class is NAD(P)H:ferrileghemoglobin oxidoreductase. This enzyme is also called ferric leghemoglobin reductase.

Role in legume nodules Leghemoglobin (Lb) is a heme-containing protein that reversibly binds and transports O2 into the N2-fixing nodules of leguminous plants. In order to function as an O2-carrier Lb must be in the ferrous oxidation state (Lb2+). Oxygenated Lb2+ (Lb2+O2) readily autoxidizes to ferric Lb (Lb3+) generating O2− in the presence of trace amounts of transition metals, chelators and toxic metabolites (such as nitrite, superoxide radical and peroxides), however Lb2+ is the predominant form in nodules. Therefore, mechanisms exist in vivo for maintaining Lb in the functional ferrous status.

History Burris and Hass were the first to propose that reduced pyridine nucleotides might function as reductants of Lb3+ in leguminous root nodules and in 1969 Appleby reported that Lb3+ was reduced to Lb2+ by a suspension of bacteroids. In 1982 Kretovich and collaborators purified an enzyme from lupine nodules which catalyzed the reduction of Lb3+ to Lb2+ using NADH as reductant. This enzyme (named by these authors as Legoglobin Reductase -LR) is similar to NADH:cytochrome b5 reductase (EC 1.6.2.2) from erythrocytes and bovine muscle. Lupin LR is a flavoprotein with a molecular mass of 60 kDa and its activity is specific for NADH. In 1984 Klucas and collaborators purified a protein with ferric Lb reductase (FLbR) activity from soybean nodules. The activity of soybean FLbR was 90% in the nodule cytosol and 10% in the bacteroids. NADH was the best reductant for soybean FLbR, although NADPH also functioned at rates that were three-fold less than NADH. These investigations by Klucas and collaborators also showed that the oxidation of NADH and reduction of Lb3+ was undetectable when O2 was removed from the reaction system, but all were restored upon re-addition of O2, which indicated that the FLbR activity is O2-dependent.

In legumes Soybean FLbR is a flavoprotein with flavin adenine dinucleotide (FAD) as the prosthetic group and consists of two identical subunits, each having a molecular mass of 54 kDa. The Km and Kcat values of soybean FLbR for soybean Lb3+ reduction are 9.2 μM and 6.2 s−1, respectively (Kcat/Km = 674 M−1 s−1). The amino acid sequence of soybean FLbR is highly related to that of the flavin-nucleotide disulfide oxidoreductases, especially dihydrolipoamide dehydrogenase (DLDH) (EC 1.8.1.4) of the pyruvate dehydrogenase complex. The amino acid sequence of soybean FLbR contains a 30-residue signal peptide for translocation into the mitochondria as well as conserved regions for the FAD-binding site, NAD(P)H-binding site and disulfide active site characteristic of pea DLDH and other enzymes in the family of the pyridine nucleotide-disulfide oxidoreductases. The soybean genome contains at least two copies (named flbr1 and flbr2) of the flbr gene. The amino acid sequence of soybean FLbR2 has considerable homology with soybean FLbR1 and pea leaf mitochondria DLDH and contains a 30-residue mitochondrial transit peptide. FLbR sequences have also been detected and analyzed in legumes other than soybean. For example, the nucleotide sequence of a cowpea FLbR cDNA has 88 and 85% similarity with soybean FLbR and pea DLDH, respectively. The Km and Kcat values of cowpea FLbR for cowpea Lb3+ reduction are 10.4 μM and 3.1 s−1, respectively (Kcat/Km = 298 M−1 s−1).

In other plants

Soybean FLbR2 reduces ferric rice Phytoglobin1.1 (Phytogb1.13+). Apparently, the soybean FLbR2-rice Phytoglobin1.13+ interaction is weak. An in silico analysis predicted that soybean FLbR2 and rice Phytogb1.13+ interact at the FAD-binding domain of soybean FLbR2 and the CD-loop and helix F of rice Phytogb1.13+. Therefore, FLbRs could be a generalized in vivo mechanism for the enzymatic reduction of Phytogbs3+.

References

Saari LL, Klucas RV (1984). "Ferric leghemoglobin reductase from soybean root nodules". Arch. Biochem. Biophys. 231 (1): 102–13. doi:10.1016/0003-9861(84)90367-9. PMID 6539095.

Illustrations

Worked examples

Example 1 — a first encounter with Leghemoglobin reductase

Start with the simplest possible case. Write down what Leghemoglobin reductase 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 Leghemoglobin reductase 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 Leghemoglobin reductase 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 Leghemoglobin reductase

In research: Leghemoglobin reductase 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 Leghemoglobin reductase 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: Leghemoglobin reductase is common in secondary-school and first-year university syllabi. It links to neighbouring topics EC 1.6.2, Enzymes of unknown structure, NADH-dependent enzymes, so understanding it makes those chapters shorter.
In everyday life: Look for Leghemoglobin reductase 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 Leghemoglobin reductase in 20 minutes

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

Frequently asked questions

What is Leghemoglobin reductase in simple terms?

In enzymology, a leghemoglobin reductase (EC 1.6.2.6) is an enzyme that catalyzes the chemical reaction NAD(P)H + H+ + 2 ferrileghemoglobin ⇌ {\displaystyle \rightleftharpoons } NAD(P)+ + 2 ferroleghemoglobin In other words, a leghemoglobin (or phytoglobin in general) with a Fe3+ is reduced to one…

Why does Leghemoglobin reductase 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 Leghemoglobin reductase?

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 Leghemoglobin reductase.