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.

Quira Zeidan

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

Join the ASBMB Today mailing list

Sign up to get updates on articles, interviews and events.

Latest in Science

Science highlights or most popular articles

St. Jude and maximizing the value of blood
Health Observance

St. Jude and maximizing the value of blood

June 14, 2021

The hospital is most renowned for passing along no costs to families. To facilitate this, the in-house capabilities of St. Jude are second to none. This includes the on-site blood donation facilities.

A balancing game with implications for neurodegenerative disease
Journal News

A balancing game with implications for neurodegenerative disease

June 8, 2021

The relationship between two proteins, one essential to mitochondrial fission and the other found in Alzheimer’s tissue, might hold the key to how disease alters the fission–fusion balance.

Can people vaccinated against COVID-19 still spread the coronavirus?
News

Can people vaccinated against COVID-19 still spread the coronavirus?

June 6, 2021

Preliminary evidence seems to suggest that someone who’s vaccinated is less likely transmit the virus, but the proof is not yet ironclad.

Addgene expands its collection into antibodies
News

Addgene expands its collection into antibodies

June 4, 2021

The reagent repository Addgene, known for distribution and quality control of plasmids for open science, is expanding into recombinant antibodies and nanobodies in partnership with NeuroMab.

Study reveals experimental targets for lymphoma research
Journal News

Study reveals experimental targets for lymphoma research

June 3, 2021

An enzyme previously linked to lymphoma development may have more functions than previously thought.

Exploring underappreciated molecules and new cities
Interview

Exploring underappreciated molecules and new cities

June 2, 2021

Neurochemist Xianlin Han has been an associate editor for the Journal of Lipid Research since 2019.