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That is an interesting suggestion, but there are some critical problems with it. Developing the functional enzyme does not appear to be a possibility in any conceivable scenario (See "Not By Chance!", a book by Lee Spetner for details). While transferring from one organism to another may in theory be possible, enzymes appear to be designed to function in ways that are too complex for such a "just so" story to be an effective explanation. For example, a biologist recently discussed the importance of the location of the enzyme within the cytoplasm in these terms: "If a scientist discovered a novel cellular protein, there are several types of questions she could ask. First, what does it do? This is the basic teleological question that drives the molecular sciences. Then, with more probing, she might ask what does it look like (that is, its primary amino acid sequence and its three dimensional structure). This helps to better answer the first question given the form-function relationship central to the molecular world. Classical biochemistry and genetics were able to deliver the answers to the first question, and better methods (gene sequencing, NMR, x-ray crystallography) have been answering the second question for the last two decades. But there is a third question to be asked that is turning out to be more important than anyone ever realized, namely, where is it? That is, the form-function relationship appears to extend beyond mere the conformation of components, but includes the actual positioning of molecules with distinct conformations.

"Let me provide a truly fascinating example of the importance of molecular positioning as expressed in the phenotype of an organism. It all starts with the metabolic reaction series known as glycolysis. Put simply, glycolysis is a ten-step reaction that partially breaks-down glucose molecules. The ten steps are catalyzed by ten distinct enzymes. One such enzyme is glycerol phosphate dehydrogenase (GPDH). Now, several years ago, a strain of fruit flies was discovered that had a mutation in this gene and, as a result, this strain was unable to fly. This was strange as glycolysis is a basic metabolic pathway used to break down sugars and generate energy and a mutation in one of its gene products that resulted only in the inability to fly was difficult to explain. After all, why was this mutation affecting only the ability to fly and not other physiological processes that would also need energy?

"Well, some elegant work was done back in 1997 that answered the question and it all has to do with positioning. To appreciate this work, two things have to be considered.

"First of all, it turns out that the enzymes that make up the glycolytic pathway are not suspended freely in the cytoplasm (a surprise to many who learned about glycolysis as undergraduate students in the 60s to 80s), but instead cling to the cytoskeleton and form larger complexes with each other that serve to channel substrates/products to each other. And many groups have shown that this takes place on the various fibers that make of the sarcomere (the basic unit of muscle contraction), among other things.

"Secondly, fruit flies have only one GPDH gene, but it exists in three isoforms. That is, one gene can give rise to three gene products because a different combination of exons are spliced together in different tissues. The three forms differ only at one terminus of the protein (they are called GPDH-1, GPDH-2, GPDH-3).

"Okay, let's put this all together. If we completely eliminate the GPDH gene from the fly's genome, the flightless phenotype appears. And when you look at the sarcomeres, two other glycolytic enzymes that normally attach are not attached.

"Now, if we take this mutant strain and give it one of the GPDH isoforms, it turns out that only *one* form will bind to the sarcomere (GPDH-1), recruit the other two glycolytic enzymes, and restore flight.

"Why is this so significant? Flies transfected with GPDH-2 or GPDH-3 have a fully functional set of glycolytic enzymes. Thus, it's not having them that counts - it's where they are put.

"This work is reviewed in:

"Srere, PA and Knull, HR. 2001. Location-location-location. TIBS 23: 319-320.

"They conclude that this work 'confirms the idea that a catalytically competent enzyme content is not sufficient for proper cell function, and that enzyme location and specific enzyme interactions are also critical for physiological function.'


'The presence of catalytically functional proteins alone is therefore not adequate; they must be properly located'

"I think this work spells out just how important the cytoskeleton is. What often determines why something is here and not there is a function of the cytoskeleton. Yet understanding why the cytoskeleton takes on this shape and not that shape, especially in light of the dynamic state of these cytoskeletal architectures, is still a black box in science. And in a sense, the cytoskeleton is a source of information.

"This work also underscores how much is involved in these Darwinian transformations. That is, it's not simply modifying an appendage in the context of an environment; it also seems to entail some subtle, but significant, remodeling of cellular states. For example, GPDH-1 is the only form used in flight muscles and is thus clearly essential to flight. Does GPDH-1 function in other muscles? I don't know, but the otherwise normal phenotype suggests it does not. If it does not, then this flight-specific form would have to evolve in concert with other macro-changes. This would involve duplicating the exon, changing it through mutations, and activating the correct pattern of alternative splicing in the appropriate tissue. And that's a long way from antibiotic resistance."

So even if it were conceivable that the enzyme could be produced by chance processes in one organism, and laterally transferred to another, this, in itself, would not necessarily be sufficient for functionality in the new organism. There is evidence for design at levels far above that we think might be just sufficient for survival. See another paper on this site, "The Trilobite: Enigma of Complexity" for further details.


Ó 2010 Arthur V. Chadwick, Ph.D.