science

Protochlorophyllide reductase

Protochlorophyllide reductase is a science 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 Protochlorophyllide reductase rather than just read about it. In short: In enzymology, protochlorophyllide reductases (POR) are enzymes that catalyze the conversion from protochlorophyllide to chlorophyllide a. They are oxidoreductases participating in the biosynthetic pathway to chlorophylls.

Key takeaways

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

Reference excerpt

In enzymology, protochlorophyllide reductases (POR) are enzymes that catalyze the conversion from protochlorophyllide to chlorophyllide a. They are oxidoreductases participating in the biosynthetic pathway to chlorophylls. There are two structurally unrelated proteins with this sort of activity, referred to as light-dependent (LPOR) and dark-operative (DPOR). The light- and NADPH-dependent reductase is part of the short-chain dehydrogenase/reductase (SDR) superfamily and is found in plants and oxygenic photosynthetic bacteria, while the ATP-dependent dark-operative version is a completely different protein, consisting of three subunits that exhibit significant sequence and quaternary structure similarity to the three subunits of nitrogenase. This enzyme may be evolutionary older; due to its bound iron-sulfur clusters is highly sensitive to free oxygen and does not function if the atmospheric oxygen concentration exceeds about 3%. It is possible that evolutionary pressure associated with the great oxidation event resulted in the development of the light-dependent system. The light-dependent version (EC 1.3.1.33) uses NADPH:

protochlorophyllide + NADPH + H+ ⇌ {\displaystyle \rightleftharpoons } chlorophyllide a + NADP+ While the light-independent or dark-operative version (EC 1.3.7.7) uses ATP and ferredoxin:

protochlorophyllide a + reduced ferredoxin + 2 ATP + 2 H2O = chlorophyllide a + oxidized ferredoxin + 2 ADP + 2 phosphate

Light-dependent The light-dependent version has the accepted name protochlorophyllide reductase. The systematic name is chlorophyllide-a :NADP+ 7,8-oxidoreductase. Other names in common use include NADPH2-protochlorophyllide oxidoreductase, NADPH-protochlorophyllide oxidoreductase, NADPH-protochlorophyllide reductase, protochlorophyllide oxidoreductase, and protochlorophyllide photooxidoreductase. LPOR is one of only three known light-dependent enzymes. The enzyme enables light-dependent protochlorophyllide reduction via direct local hydride transfer from NADPH and a longer-range proton transfer along a defined structural pathway. LPOR is a ~40kDa monomeric enzyme, for which the structure has been solved by X-ray crystallography. It is part of the SDR superfamily, which includes alcohol dehydrogenase, and consists of a Rossman-fold NADPH-binding site and a substrate-specific C-terminal segment region. The protochlorophyllide substrate is thought to bind to a cavity near the nicotinamide end of the bound NADPH. LPOR is primarily found in plants and oxygenic photosynthetic bacteria, as well as in some algae.

Light-independent The light-independent version has the accepted name of ferredoxin:protochlorophyllide reductase (ATP-dependent). Systematically it is known as ATP-dependent ferredoxin:protochlorophyllide-a 7,8-oxidoreductase. Other names in common use include light-independent protochlorophyllide reductase and dark-operative protochlorophyllide reductase (DPOR). DPOR is a nitrogenase homologue and adopts an almost identical overall architecture arrangement to both nitrogenase as well as the downstream chlorophyllide a reductase (COR). The enzyme consists of a catalytic heterotetramer and two transiently-bound ATPase dimers (right). Similar to nitrogenase, the reduction mechanism relies on an electron transfer from the iron-sulfur cluster of the ATPase domain, through a secondary cluster on the catalytic heterotetramer and finally to the protochlorophyllide-bound active site (which, distinct from nitrogenase, does not contain FeMoco). The reduction requires significantly less input than the nitrogenase reaction, requiring only a 2-electron reduction and 4 ATP equivalents, and as such may require an auto-inhibitory mechanism to avoid over-activity. DPOR can alternatively take as its substrate the compound with a second vinyl group (instead of an ethyl group) in the structure, in which case the reaction is

3,8-divinylprotochlorophyllide + reduced ferredoxin + 2 ATP + 2 H2O ⇌ {\displaystyle \rightleftharpoons } 3,8-divinylchlorophyllide a + oxidized ferredoxin + 2 ADP + 2 phosphate This enzyme is present in photosynthetic bacteria, cyanobacteria, green algae and gymnosperms.

Illustrations

Worked examples

Example 1 — a first encounter with Protochlorophyllide reductase

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

In research: Protochlorophyllide reductase appears in science 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 Protochlorophyllide 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: Protochlorophyllide reductase is common in secondary-school and first-year university syllabi. It links to neighbouring topics EC 1.3.1, EC 1.3.7, NADPH-dependent enzymes, so understanding it makes those chapters shorter.
In everyday life: Look for Protochlorophyllide 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.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Protochlorophyllide reductase in 20 minutes

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

Frequently asked questions

What is Protochlorophyllide reductase in simple terms?

Why does Protochlorophyllide reductase matter?

Because it connects several science 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 Protochlorophyllide 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 Protochlorophyllide reductase.