CO sniffing through heme-based sensor proteins

O-2, NO, and CO are substrates, products, and/or modulators in many enzymatic reactions including O-2 respiration, denitrification, N-2 fixation, and methanogenesis. Over the last decade, O-2, NO, and CO have been reported to act as signaling molecules in the control of several distinct biological functions. Here, the heme-based mechanisms of CO sensing by the bacterial homodimeric CooA and the mammalian heterodimeric NPAS2-BMAL1 transcriptional factors are reviewed, and the signal transduction pathways are discussed.