23 Sep

Toxic Forms of Oxygen

Toxic forms of oxygen are produced in aerobic environments during photochemistry and is a result of aerobic respiration.  Hydrogen peroxide is a by-product of aerobic respiration and can severely damage proteins.  Singlet oxygen and anion superoxide are also forms of toxic oxygen and damage other molecules.  Aerobic bacteria have developed protein systems involving enzymes to convert toxic forms of oxygen to less harmful compounds.  Aerobes contain enzyme catalase, which degrades hydrogen peroxide into oxygen and water.  They also contain superoxide dismutase which converts superoxide to oxygen and hydrogen peroxide which can be removed by catalase.  Peroxidase is another enzyme utilized by anaerobes which requires the coenzyme NAD+ to break down hydrogen peroxide into water.  Aerotolerant aerobes lack catalse but they possess superoxide dismutase or other mechanisms to deal with superoxide.  Strict anaerobes do not possess either catalase or superoxide dismutase but some may have alternative enzymes to deal with superoxide.  The sensitivity of anaerobes to oxygen is a multifactorial problem that includes but is not limited to the absence of detoxifying enzymes such as catalse and superoxide dismutase.