Difference Between Cytochrome and Phytochrome

The key difference between cytochrome and phytochrome is that cytochrome is an electron transfer heme protein involved in aerobic respiration. Meanwhile, phytochrome is a photoreceptor protein that is sensitive to red and far-red light of the visible spectrum.

Living organisms have different types of pigments. Some are light-absorbing pigments while some are respiratory pigments. Cytochrome is a metalloprotein that works as an electron carrier in aerobic respiration. Meanwhile, phytochrome is a photoreceptor which absorbs red and far-red light from the visible spectrum. Compared to cytochrome, phytochromes are important in many aspects of plant development.

CONTENTS

1. Overview and Key Difference
2. What is Cytochrome
3. What is Phytochrome
4. Similarities Between Cytochrome and Phytochrome
5. Side by Side Comparison – Cytochrome vs. Phytochrome in Tabular Form
6. Summary

What is Cytochrome?

Cytochromes are a protein complex that acts as an electron carrier in the electron transport chain. They are loosely associated with the inner membrane of the mitochondria. They are small heme proteins. Cytochromes serve as extreme important electron carriers since they facilitate the handover of electrons to a final electron acceptor (O₂) in order to complete aerobic respiration.

There are three main cytochromes as cytochrome reductase, cytochrome c, and cytochrome oxidase. Cytochrome reductase receives electrons from ubiquinone and transfers to cytochrome c. Cytochrome c transfers an electron to cytochrome oxidase. Cytochrome oxidase passes electrons to O₂ (the final electron acceptor). When electrons travel through electron carriers, a proton gradient will be created, and it will help the ATP production.

What is Phytochrome?

Phytochrome is a photoreceptor found in plants, fungi, and bacteria. It was discovered by Sterling Hendricks and Harry Borthwick. Phytochromes can detect light in the range of red and far-red regions of the visible spectrum. Hence, the phytochrome system works as a red light-sensitive system in plants. During the daytime, by absorbing red light wavelength, phytochrome r becomes phytochrome fr. During the nighttime, by absorbing the far-red light, phytochrome fr become photochrome r. Thus, Pr is a less active basic form, while Pfr is a hyperactive form of phytochrome. Moreover, phytochromes act as temperature sensors. Structurally phytochrome is a protein molecule (a dimer of two identical 124 kDa polypeptides) with a chromophore, which is covalently bonded to the protein.

Phytochromes are important for several aspects of plant development, including seed germination, stem elongation, leaf expansion, the formation of certain pigments, chloroplast development, and flowering. Moreover, phytochromes affect root growth. There are five phytochromes.

What are the Similarities Between Cytochrome and Phytochrome?

• Both cytochrome and phytochrome are proteins.
• Cytochrome is a respiratory pigment, while phytochrome is a photopigment.

What is the Difference Between Cytochrome and Phytochrome?

Cytochrome is a heme protein involved in the electron transport chain as an electron carrier. Meanwhile, photochrom is a photoreceptor found in plants, bacteria, and fungi, which absorbs red and far-red light from the visible light. So, this is the key difference between cytochrome and phytochrome.

Moreover, cytochromes are present in animals, while phytochromes are absent in animals. Therefore, this is also a difference between cytochrome and phytochrome.

Summary – Cytochrome vs. Phytochrome

Cytochrome is a heme protein needed for aerobic respiration. It works as an electron transfer protein. In contrast, phytochrome is a photoreceptor protein that is important for many aspects of plant development, especially photomorphogenic aspects. Phytochromes are found in plants, bacteria and fungi while cytochromes are found in plants and animals. Thus, this summarizes the difference between cytochrome and phytochrome.

Reference:

1. Li, Jigang, et al. “Phytochrome Signaling Mechanisms.” The Arabidopsis Book, American Society of Plant Biologists, 2011, Available here.
2. “Cytochrome.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 4 Dec. 2018, Available here.

Image Courtesy:

1. “Cytochrome c” By Klaus Hoffmeier – Own work (Public Domain) via Commons Wikimedia
2. “3G6O.pdb” By Jmol Development Team – Jmol (GPL) via Commons Wikimedia