Odd Roles for Atmospheric Molecules In the Human Body

Molecules that were once associated mainly with the atmosphere have turned out to be produced naturally in our bodies, playing a wide and wild assortment of roles. For instance, in the mid 1980’s and early 1990’s, NO (nitrous oxide), a common pollutant, was shown to be synthesized in the body from the amino acid (arginine).

Model of the amino acid, arginine. An enzyme NO synthase converts arginine to citrulline. The  carbon atom labeled with a red C has one of its amino groups(NH2) replaced with a carbonyl. The amino group is what’s oxidized to nitrogen monoxide.


Nitrous oxide is a blood vessel dilator, allowing  the penis’ limp flesh to engorge with blood and mushroom into a rigid, functional form. It also acts as a neurotransmitter in some parts of the brain, permitting peristalsis in the esophagus.


In the early 2000s, Scripps Research Institute chemists and others discovered that antibodies appear to catalyze the formation of ozone(O3). They also showed that this important stratospheric UV filter but ground-level pollutant is biosynthesized within arteries by atherosclerotic plaques. In the former case, antibodies first produce the short-lived H2O3 molecule, which then breaks down in the following overall reaction:
H2O3 -> O2 + H2O2 + O3

Ozone in aqueous systems is short-lived, with a half life of only a minute, which is probably adequate for killing unwanted invaders. The  production of peroxide alone is not sufficient to kill bacteria.

You will notice that the above overall  reaction is not balanced.
There are several ways of balancing the equation without creating redundant solutions.
n H2O3 -> xO2 + n H2O2 + y O3
3n = 2x + 2n + 3y
n = 2x + 3y
if x = y =1, then n = 5; if x = 2 and y = 1, then n = 7; etc…producing
5 H2O3 -> O2 + 5 H2O2 + O3
7 H2O3 -> 2O2 + 7 H2O2 + O3

There are of course many other solutions. Which is the real overall equation? Perhaps they are all wrong. In a paper published this year Arnold N. Onyango argued that  H2O3 decomposes far too readily in water to form singlet O2 and water, rather than O3 and H2O2. He points out that the literature seems to better support an alternative hypothesis. Ozone can have an amino acid origin, analaogous to the way NO is produced. The progenitors instead could be the  amino acids methionine, tryptophan, histidine, and cysteine. When oxidized by O2 in a high energy state (so-called singlet oxygen 1O2  or 1Δg ) small amounts of ozone could be produced.





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