Iron is the most abundant element on earth representing nearly 90% of the mass in the
earth’s core, yet only trace elements are present in living cells. Most of the iron in the
body is located within the porphyrin ring of heme, which is incorporated into proteins
such as hemoglobin, myoglobin, cytochromes, catalases and peroxidases. Although
iron appears in a variety of oxidation states, in particular as hexavalent ferrate, the
ferrous and ferric forms are of most importance.
Iron regulatory protein-1 binding to the iron-responsive element of mRNA
is sensitive to iron, oxidative stress, NO, and hypoxia. Each of these agents
changes the level of intracellular ATP, suggesting a link between iron levels
and cellular energy metabolism.
Amongst a wide variety of different biochemical reactions in cellular car-bon metabolism, thiamin diphosphate-dependent enzymes catalyze the oxi-dative decarboxylation of 2-keto acids. This type of reaction typically
involves redox coupled acyl transfer to CoA or phosphate and is mediated
by additional cofactors, such as flavins, iron-sulfur clusters or lipoamide
swinging arms, which transmit the reducing equivalents that arise during
keto acid oxidation to a final electron acceptor.