Ann Gauger was reading a cell paper the other day [Digging Deep in Biology: "Things Get Even More Complicated When You Look Closer"]. The subject was the localization of citric acid cycle enzymes and pyruvate dehydrogenase (PDH). She did a little digging and this is what astonished her ...
... so I looked up pyruvate dehydrogenase and found to my astonishment that it is not one enzyme but an enormous complex of three different enzymatic activities clustered together on a cube-shaped core of 24 units, or alternatively a dodecahedral core of 60 units. The enzymes work together to turn pyruvate into acetyl CoA in a three-step process, handing off to each other as the reaction proceeds.Theme
Pyruvate DehydrogenaseAnn Gauger has a B.S. in biology and a Ph.D. in developmental biology (1989). I can understand how she might have forgotten details about biochemistry and metabolism but I'm sure that at one point she was taught correctly. The idea that she would be "astonished" at the structure and function of pyruvate dehydrogenase is itself astonishing. It's described in all the biochemistry textbooks. You may have forgotten what you learned but surely a memory jog doesn't count as "astonishment"?
Ann Gauger is an Intelligent Design Creationist who thinks that God created Adam and Eve. From her perspective, the most astonishing thing about her discovery is not that this is common knowledge among today's undergraduates but that she can spin it into support for her creationist views.
Let me emphasize: this is a core enzymatic activity. The TCA cycle is important to the process by which cells make ATP, the energy currency of the cell. PDH is the link that connects glycolysis, the breakdown of sugars, to the TCA cycle. Without it cells would obtain much less energy from the breakdown of sugars. But it is also essential for embryonic development past the two- to four-cell stage (in mice and humans, and presumably other mammals).She tells us in the update on her post that she checked a biochemistry textbook after writing this so at least she's done a bit of after-the-fact checking. But normally a scientist does a bit more research before advancing a claim as radical as the one she advances; namely, that there's no evolutionary explanation for pyruvate dehydrogenase.
It's also essential for bacteria like E. coli, where it has a similar structure and three-step reaction. This is an ancient enzyme complex, yet of great sophistication.
How could early cells have assembled such a structure, bringing together separate enzyme activities to work cooperatively? Getting enzymes to assemble into multi-subunit structures is non-trivial, requiring multiple side-chain interactions and three-dimensional fit. Even further, the genes encoding these enzymatic activities of the PDH complex are clustered together into a single operon in E. coli. They are neighbors, side-by-side in E. coli's genome, and co-expressed. Of course, that's how an intelligent designer would do it. What's the use of part of a complex? Make the enzymes together and assemble them into a factory to turn pyruvate into acetyl CoA -- it's much more efficient.
Let's look at another textbook to see if there are any clues that might have helped her.1
A similar pyruvate dehydrogenase complex is present in many species of bacteria although some, such as gram-negative bacteria, have a smaller version where there are only 24 E2 enzymes in the core. In these bacteria, the core enzymes are arranged as a cube with one trimer at each of the eight vertices. The E2 subunits of the two different bacterial enzymes and the eukaryotic mitochondrial and chloroplast versions are all closely related. However, the gram-negative bacterial enzymes contain E1 enzymes that are unrelated to the eukaryotic versions.She could have learned several things by reading my undergraduate textbook.
Pyruvate dehydrogenase is a member of a family of multienzyme complexes known as the 2-oxo acid dehydrogenase family. (Pyruvate is the smallest 2-oxo organic acid.) We will encounter two other 2-oxo (or α-keto) acid dehydrogenases that closely resemble pyruvate dehydrogenase in structure and function. One is a citric acid cycle enzyme, α-ketoglutarate dehydrogenase (Section 13.3#4), and the other is branched chain α-keto acid dehydrogenase, used in amino acid metabolism (Section 17.10E). All members of the family catalyze essentially irreversible reactions in which an organic acid is oxidized to CO2 and a coenzyme A derivative is formed.
The reverse reactions are catalyzed in some bacteria by entirely different enzymes. These reactions form part of a pathway for fixing carbon dioxide in anaerobic bacteria. Some bacteria and some anaerobic eukaryotes convert pyruvate to acetyl CoA and CO2 using pyruvate:ferredoxin 2-oxidoreductase, an enzyme that is unrelated to pyruvate dehydrogenase.
1. More simple versions of this enzyme exist in bacteria suggesting strongly that the complex version in mammals evolved from a simpler version and there may be even more simple versions in other bacteria.
2. Separate E1 subunits may have evolving several times independently. A little digging in the scientific literature would have uncovered more information about their evolution.
3. There are two other related enzymes in most cells. A simple google search would have uncovered a post I wrote ten years ago [Pyruvate Dehydrogenase Evolution]. I explained that the available evidence (sequence comparisons, etc.) suggest strongly that the common form of modern pyruvate dehydrogenase evolved from a primitive version of branched chain α-keto acid dehydrogenase, a key enzyme in amino acid biosynthesis.
4. Some bacteria have a different enzyme that catalyzes the same reaction: pyruvate:ferredoxin 2-oxidoreductase. This suggests that the earliest cells probably used this enzyme and the modern version of pyruvate dehydrogenase evolved later. (There's plenty of evidence supporting the idea that ferredoxin enzymes were the first oxidation-reduction enzymes.)
I'm not saying we have definitive proof of a stepwise evolutionary pathway to the first complex form of branched chain α-keto acid dehydrogenase and from there to the complex modern version of pyruvate dehydrogenase. These scenarios are speculative, but they are plausible. The fact that we have plausible, naturalistic, explanations for the evolution of pyruvate dehydrogenase means that we have no need of Ann Gauger's god(s).
But here's the more important point. She could have easily uncovered all this information by herself in just a few hours (at most). Why do Intelligent Design Creationists always assume that a gap in their own knowledge means that nobody knows anything about the subject?
And why do they always go on to fill these gaps with god(s)?
1. Moran, L.A., Horton, H.R., Scrimgeour, K.G., and Perry, M.D. (2012) Principles of Biochemistry 5th ed., Pearson Education Inc. © Pearson/Prentice Hall