A Year of (Bio)chemical Elements

For February, it’s iron — atomic No. 26

Quira Zeidan
Feb. 1, 2019

Hemoglobin is a tetramer that consists of four polypeptide chains. Each monomer contains a heme group in which an iron ion is bound to oxygen. In iron-deficiency anemia, the heart works harder to pump more oxygen through the body, which often leads to heart failure or disease.We are celebrating the 150th anniversary of Mendeleev’s periodic table by highlighting one or more chemical elements with important biological functions each month in 2019. For January, we featured atomic No. 1 and dissected hydrogen’s role in oxidation-reduction reactions and electrochemical gradients as driving energy force for cellular growth and activity.

Iron

In February, we have selected iron, the most abundant element on Earth, with chemical symbol Fe (from the Latin word “ferrum”) and atomic number 26.

A neutral iron atom contains 26 protons and 30 neutrons plus 26 electrons in four different shells around the nucleus. As with other transition metals, a variable number of electrons from iron’s two outermost shells are available to combine with other elements. Commonly, iron uses two (oxidation state +2) or three (oxidation state +3) of its available electrons to form compounds, although iron oxidation states ranging from -2 to +7 are present in nature.

Iron occurs naturally in the known universe. It is produced abundantly in the core of massive stars by the fusion of chromium and helium at extremely high temperatures. Each of these supergiant, iron-containing stars only lives for a brief while before violently blasting as a supernova, scattering iron into space and onto rocky planets like Earth. Iron is present in the Earth’s crust, core and mantle, where it makes up about 35 percent of the planet’s total mass.

Iron is crucial to the survival of all living organisms. Biological systems are exposed constantly to high concentrations of iron in igneous and sedimentary rocks. Microorganisms can uptake iron from the environment by secreting iron-chelating molecules called siderophores or via membrane-bound proteins that reduce Fe+3 (ferric iron) to a more soluble Fe+2 (ferrous iron) for intracellular transport. Plants also use sequestration and reduction mechanisms to acquire iron from the rhizosphere, whereas animals obtain iron from dietary sources.

Once inside cells, iron associates with carrier proteins and with iron-dependent enzymes. Carrier proteins called ferritins (present in both prokaryotes and eukaryotes) store, transport and safely release iron in areas of need, preventing excess free radicals generated by high-energy iron. Iron-dependent enzymes include bacterial nitrogenases, which contain iron-sulfur clusters that catalyze the reduction of nitrogen (N2) to ammonia (NH3) in a process called nitrogen fixation. This process is essential to life on Earth, because it’s required for all forms of life for the biosynthesis of nucleotides and amino acids.

Some iron-binding proteins contain heme — a porphyrin ring coordinated with an iron ion. Heme proteins include cytochromes, catalase and hemoglobin. In cytochromes, iron acts as a single-electron shuttle facilitating oxidative phosphorylation and photosynthesis reactions for energy and nutrients. Catalase iron mediates the conversion of harmful hydrogen peroxide to oxygen and water, protecting cells from oxidative damage. In vertebrates, the Fe+2 in hemoglobin is reversibly oxidized to Fe+3, allowing the binding, storage and transport of oxygen throughout the body until it is required for energy production by metabolic oxidation of glucose.

Living organisms have adapted to the abundance and availability of iron, incorporating it into biomolecules to perform metal-facilitated functions essential for life in all ecosystems.

Enjoy reading ASBMB Today?

Become a member to receive the print edition monthly and the digital edition weekly.

Learn more
Quira Zeidan

Quira Zeidan is the ASBMB’s education and public outreach coordinator.

Get the latest from ASBMB Today

Enter your email address, and we’ll send you a weekly email with recent articles, interviews and more.

Latest in Science

Science highlights or most popular articles

Drugs of the future will be easier and faster to make, thanks to mRNA
News

Drugs of the future will be easier and faster to make, thanks to mRNA

Feb. 25, 2024

But researchers still have to work out a few remaining kinks.

Mouse model may help explain, treat infertility
Journal News

Mouse model may help explain, treat infertility

Feb. 24, 2024

Discovering how sperm begin the fertilization process could also identify new targets for nonhormonal contraceptives.

AI harnesses tumor genetics to predict treatment response
News

AI harnesses tumor genetics to predict treatment response

Feb. 18, 2024

Many paths lead to cancer resistance; artificial intelligence can decode them all simultaneously.

Progression of ALS linked to a membrane and an enzyme
News

Progression of ALS linked to a membrane and an enzyme

Feb. 17, 2024

Diminished activities of the enzyme TBK1 in mitochondrial-associated membrane reduces motor neurons’ tolerance to stressors, a causative factor in the disease.

From the journals: JLR
Journal News

From the journals: JLR

Feb. 16, 2024

Breaking down atherosclerotic plaque. Location matters in liver disease. A lipidomic profile drives liver disease. Read about recent papers on these topics.

Sibling study reveals mechanism for genetic disease
Journal News

Sibling study reveals mechanism for genetic disease

Feb. 13, 2024

Using proteomics experiments, researchers found that old proteins pile up in the mitochondria of people with a form of adult-onset muscular dystrophy.