Two Predictions

If you watched the last animation, you know that cytochrome oxidase plays the key role in aerobic respiration. Not only is it a proton pump like the other complexes, but it accepts the high energy electrons and passes them to oxygen, the final electron acceptor.

So when did cytochrome oxidase appear?

According to traditional textbook explanations, cytochrome oxidase evolved after the emergence of oxygenic photosynthetic. As one team of researchers explain:

Present-day atmospheric oxygen originates mainly from water photolysis through the oxygenic photosynthetic activity of Cyanobacteria and photosynthetic eukaryotes (with their chloroplasts of cyanobacterial origin), whereas the abiotic production of O2 from water photolysis by UV light is considered negligible. Following this logic, it is generally assumed that aerobic respiration arose only after the appearance of oxygenic photosynthesis, in response to the accumulation of biologically produced O2 (Battistuzzi et al. 2004). [1]

Or, to put it more simply,

it was tacitly assumed that oxygenic photosynthesis had to evolutionarily precede aerobic respiration, since the latter requires a substrate, O2, produced by the first. [2]

From a conventional, non-telic perspective, this makes sense as a prediction. Consider again the relationship between respiration and photosynthesis.

Cytochrome oxidase uses oxygen as its substrate and photosynthesis emits it as its product. Thus photosynthesis would change the environment, creating the selective pressure to evolve the oxidase. It is no surprise that this non-teleological prediction became conventional wisdom.

But the perspective of front-loading would allow us to make a more radical prediction. If photosynthesis was part of the objective of terraforming, and terraforming was linked to front-loading, we would predict the oxidase existed “in waiting.” In other words, it existed either prior to or along side photosynthesis. Aerobic respiration, needed for complex metazoan life to emerge and exist, was in the cards.

So which prediction has born out?

1. Brochier-Armanet C, Talla E, Gribaldo S. 2009. The multiple evolutionary histories of dioxygen reductases: Implications for the origin and evolution of aerobic respiration. Mol Biol Evol. 26:285-97.

2. Schütz M, Brugna M, Lebrun E, Baymann F, Huber R, Stetter KO, Hauska G, Toci R, Lemesle-Meunier D, Tron P, Schmidt C, Nitschke W. 2000. Early evolution of cytochrome bc complexes. J Mol Biol. 300:663-75.

5 responses to “Two Predictions

  1. I give up, “So which prediction has born out?”

  2. Been super busy. I’ll try to resume this on the weekend.

  3. I’ll hold my breath.

  4. Are you turning blue yet?

  5. I cheated.

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