We can't live without oxygen. Our cells rely on oxygen as the final acceptor of electrons in respiration, allowing us to extract far more energy from food than possible without oxygen. But oxygen is also a dangerous compound. Reactivating with other molecules can produce reactive oxygen species (ROS) that can damage cells. Our cells have evolved multiple mechanisms to prevent this damage to keep ROS levels in check.
One meaningful way that cells control ROS levels is through antioxidant enzymes. Antioxidants are substances that can prevent or slow damage to cells caused by free radicals, unstable molecules that the body produces as a response to environmental and other pressures. The body also needs antioxidant enzymes to clean up these dangerous molecules.
There are many types of antioxidant enzymes, each with a specific role in protecting cells from ROS. One necessary type of antioxidant enzyme is superoxide dismutase (SOD). Dismutase, in this context, means to break down, and SOD breaks down SO into oxygen and hydrogen peroxide. While hydrogen peroxide is a reactive compound, it is not as reactive as superoxide; it can still damage cells. Another type of antioxidant enzyme, catalase, breaks down hydrogen peroxide into water and oxygen to prevent this. SOD and catalase are just two of the many antioxidant enzymes that our cells use to control ROS levels. These enzymes are essential for keeping our cells healthy and preventing disease.
Cu/Zn superoxide dismutase is a very efficient enzyme.
Zn is an essential mineral for the body because it helps to protect cells from damage. Researchers have determined that one out of every ten collisions between superoxide (SO) and the enzyme will lead to a reaction. It is far more than expected since the active site covers only a tiny portion of the enzyme surface, and we might expect that most collisions would occur somewhere else on the surface.
However, the active site's shape and characteristics may give some hints to this efficiency. The active site is funnel-shaped, with copper and zinc (colored green here) at the base of the funnel. The strong positive charge of the metal ions, along with two nearby positively charged amino acids (colored blue here), draw the negatively charged SO (red) into the funnel.
SOD has recently gained notoriety for its connection with amyotrophic lateral sclerosis, more commonly known as Lou Gehrig's disease. Recent research has shown that one of the mutations is found in the gene for SOD. Scientists are now studying the role of SOD in the disease, hoping that this knowledge will lead to new treatments and cures.
The list of pathophysiological conditions associated with the overproduction of SO anions expands daily. The most exciting realization is that there is a similarity between the tissue injury observed in various disease states, as SO anions produce tissue injury and associated inflammation in all tissues in similar ways.
Tissue injury and inflammation form the basis of many disease pathologies, including ischemia and reperfusion injuries, radiation injury, hyperoxic lung damage, and atherosclerosis. This commonality provides a unique opportunity to manipulate numerous disease states with an agent that removes SO anions.