Posted on 11/16/2008 8:19:06 PM PST by Maelstorm
All biological reactions within human cells depend on enzymes. Their power as catalysts enables biological reactions to occur usually in milliseconds. But how slowly would these reactions proceed spontaneously, in the absence of enzymes – minutes, hours, days? And why even pose the question?
One scientist who studies these issues is Richard Wolfenden, Ph.D., Alumni Distinguished Professor Biochemistry and Biophysics and Chemistry at the University of North Carolina at Chapel Hill. Wolfenden holds posts in both the School of Medicine and in the College of Arts and Sciences and is a member of the National Academy of Sciences.
In 1995, Wolfenden reported that without a particular enzyme, a biological transformation he deemed "absolutely essential" in creating the building blocks of DNA and RNA would take 78 million years.
"Now we've found a reaction that – again, in the absence of an enzyme – is almost 30 times slower than that," Wolfenden said. "Its half-life – the time it takes for half the substance to be consumed – is 2.3 billion years, about half the age of the Earth. Enzymes can make that reaction happen in milliseconds."
With co-author Charles A. Lewis, Ph.D., a postdoctoral scientist in his lab, Wolfenden published a report of their new findings recently in the online early edition of the Proceedings of the National Academy of Science. The study is also due to appear in the Nov. 11 print edition.
The reaction in question is essential for the biosynthesis of hemoglobin and chlorophyll, Wolfenden noted. But when catalyzed by the enzyme uroporphyrinogen decarboxylase, the rate of chlorophyll and hemoglobin production in cells "is increased by a staggering factor, one that's equivalent to the difference between the diameter of a bacterial cell and the distance from the Earth to the sun."
"This enzyme is essential for both plant and animal life on the planet," Wolfenden said. "What we're defining here is what evolution had to overcome, that the enzyme is surmounting a tremendous obstacle, a reaction half-life of 2.3 billion years."
Knowing how long reactions would take without enzymes allows biologists to appreciate their evolution as prolific catalysts, Wolfenden said. It also enables scientists to compare enzymes with artificial catalysts produced in the laboratory.
"Without catalysts, there would be no life at all, from microbes to humans," he said. "It makes you wonder how natural selection operated in such a way as to produce a protein that got off the ground as a primitive catalyst for such an extraordinarily slow reaction."
Experimental methods for observing very slow reactions can also generate important information for rational drug design based on cellular molecular studies.
"Enzymes that do a prodigious job of catalysis are, hands-down, the most sensitive targets for drug development," Wolfenden said. "The enzymes we study are fascinating because they exceed all other known enzymes in their power as catalysts."
Wolfenden has carried out extensive research on enzyme mechanisms and water affinities of biological compound. His work has also influenced rational drug design, and findings from his laboratory helped spur development of ACE inhibitor drugs, now widely used to treat hypertension and stroke. Research on enzymes as proficient catalysts also led to the design of protease inhibitors that are used to treat HIV infection.
"We've only begun to understand how to speed up reactions with chemical catalysts, and no one has even come within shouting distance of producing, or predicting the magnitude of, their catalytic power," Wolfenden said.
Creation of life? The first living things are not proposed to have either hemoglobin (for carrying oxygen) or chlorophyll (for photosynthesis).
Obstacles?
I doubt that Genesis will ever be discovered, for then we’d by that reason, know what lies beyond life as well.
Helps one appreciate the impossibility of the spontaneous generation of life...it couldn’t happen by accident...it couldn’t happen by chance!
Hmm...fascinating, the more we know, the less we know..
Precisely. Evolution is a much more reasonable explanation than creation.
No, but it does help one appreciate the virtual impossibility of the spontaneous generation of life based around hemoglobin or clorophyll. Note, however, that the only people making that absurd claim are creationists. Reasonable people believe that complex biological systems evolved over time using well understood mechanisms.
Evolution is an awesome process. No wonder God chose it.
It depends on what flavor of Evolution one supports. Undirected evolution is not reasonable in the least.
If the codependent proteins were to synthesize simultaneously and be placed in the proper relationship to each other, like auto parts on an assembly line with a downhill slope, then life could arise spontaneously. That wouldn’t require any intelligent design at all.
How convenient - you changed the subject. I was talking about the origin of life, and you replied with a comment about life evolving...and said nothing about the origin of life. Pretty fast work.
I just double checked and didn't see uroporphyrinogen decarboxylase mentioned in the Bible.
Please elaborate on these "well understood mechanisms" you speak of. For example describe the stociometric conditions that enabled self-sytheses of complex biomolecues and how reaction pathways "evolved", how did the huge obstacle of activation energies for reactions necessary in systhsizing these biomolecules were overcome in the absence of appropriate catalysis, and finally how is it that these systems evolve over great spans of time when organic biomolecules have relatively short shelf-life (hours, days maybe) before they degrade or become denatured. Are you talking about in-vitro systems or in-vivo systems that are so well understood?
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