Organic and Inorganic Chemistry

Inorganic Materials and Nanoparticles

Transition metals are usually present as trace elements in organisms, with iron and zinc being most abundant. These metals are used in some proteins as cofactors and are essential for the activity of enzymes such as catalase and oxygen-carrier proteins such as hemoglobin. Metal homeostasis is broadly defined as the metal uptake, trafficking, efflux, and sensing pathways that allow organisms to maintain an appropriate often narrow intracellular concentration range of essential transition metals. Metal centers are essential and abundant cofactors in fundamental life processes such as photosynthesis, respiration, and hydrogen, nitrogen carbon, and sulfur metabolism, and the number and diversity of metalloproteins and the biological roles for metal centers continue to proliferate unabated. Indeed, metal centers are estimated to be present in approximately one half of all proteins and to constitute the active sites of at least one third of all enzymes. Metalloprotein is a generic term for a protein that contains a metal ion cofactor. A large number of all proteins are part of this category. Metalloproteins have captivated chemists and biochemists, particularly since the 1950s, when the first X-ray crystal structure of a protein, sperm whale myoglobin, indicated the presence of an iron atom. They account for nearly half of all proteins in nature. Transition metals are a key component of biological systems. Because of their special properties, they are incorporated into proteins functioning in dioxygen transport, electron transfer, redox transformations, and regulatory control. The metals used in biological systems have been selected throughout evolution based on their availability in the environment and their kinetic lability, resulting in preferential use of first-row transition metals in biology.