The Miracle of the Cell by Michael Denton

The Miracle of the Cell by Michael Denton

Author:Michael Denton [Denton, Michael]
Language: eng
Format: azw3, epub
ISBN: 9781936599851
Publisher: Discovery Institute
Published: 2020-09-28T00:00:00+00:00


Figure 6.3. Rendering of human carbonic anhydrase II.

CO2 + H2O = H2CO3 → CO2 + H2O

In the tissues—In the lungs

Carbonic anhydrase also aids in the regulation of fluid and pH balance and is involved in producing essential stomach acid. The enzyme also plays a role in vision. When it is defective, fluid can build up and cause glaucoma. The enzyme is one of the fastest known, catalyzing up to one million reactions per second.60

Might zinc be indispensable for this reaction? The evolutionary evidence suggests very strongly that this is likely. There are many types of carbonic anhydrase with no amino acid sequence similarities, suggesting that the enzyme has arisen many times independently in the history of life. But almost all have a similar active site, which contains zinc bonded to three nitrogen atoms in three histidine amino acids in the protein.

The discovery in 2008 that a marine unicellular organism can use cadmium (Cd) instead of zinc in certain circumstances suggests that zinc isn’t uniquely required in carbonic anhydrase.61 However, this discovery is not as radical as might appear, since cadmium is the homologue of zinc in period five of the periodic table. While the discovery does nuance our understanding, the result actually tends to confirm the claim that particular biological functions depend on particular metal ions. For one thing, the same basic active site was arrived at multiple times in evolution. For another thing, even though zinc and cadmium are exceedingly rare in some environments, no organism in billions of years of evolution has employed an alternative to zinc or cadmium. The implication is that only zinc or its close homologue can carry out this specific reaction with such extraordinary efficiency, a reaction that enables us to rid ourselves of some 100 million trillion molecules of CO2 every breath.62

To briefly summarize before moving on to the final metal in this chapter: One metal, manganese, gives us oxygen. Two other metals, iron and copper, give us electron transport chains, proton pumping, and ATP. The oxidation of hydrocarbons in the mitochondria gives us H2O and CO2. And CO2 requires another metal atom, zinc, if it is to be excreted from the body in the lungs. Together these provide powerful evidence for a stunning prior fitness in nature for aerobic life.

Molybdenum

ANOTHER TRANSITION metal necessary to life (and an essential nutrient in the human diet) is molybdenum (Mo). It occurs in four important enzymes in our bodies (sulfite oxidase, aldehyde oxidase, xanthine oxidase, and mitochondrial amidoxime reductase). People who don’t get enough of it can suffer many adverse effects.63

Molybdenum also is involved in a vital activity upon which all life on Earth depends: nitrogen fixation. This process is carried out by the enzyme nitrogenase, which catalyzes the reduction of nitrogen to ammonia. Virtually all the nitrogen used by living things is initially captured by the work of this vital enzyme.

Nitrogenase fixes atmospheric nitrogen (N2) by breaking the triple N bond which links the two nitrogen atoms together, reducing the nitrogen to ammonia NH3. This is the compound through which the nitrogen atom is introduced into the organic domain.



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