Bioinorganic chemistry
Oxygen transport and activation proteins: these make use of metals such as iron, copper, and manganese.  Heme is used by red blood cells in the form of hemoglobin for oxygen transport.  Other oxygen transport systems include myoglobin, hemocyanin, and hemerythrin.  Oxidases and oxygenases are metal systems found throughout nature that take advantage of oxygen to carry out important reactions such as energy generation.  Some metalloproteins are designed to protect a biological system from the potentially harmful effects of oxygen and other reactive oxygen-containing molecules such as hydrogen peroxide. A complementary metalloprotein to those that react with oxygen is chlorophyll, the basis of photosynthesis. Chlorophyll is a carbon ring pigment, similar to other porphyrin pigments such as heme. At the center of the chlorin ring is a magnesium ion. This system is part of the complex protein machinery that produces oxygen as plants do photosynthesis.