Re: How do we know the specifics about the electron transport chain?

Michael:

I sincerely apoogize for the delay in responding to your inquiry, questions about the history behind science are actually some of my favorite to answer. You are absolutely correct in that the variety of biochemical reactions occuring within a cell is nearly daunting, and the elucidation of these reactions, pathways and products was performed by many individuals, several of whom recieved Nobel Prizes for their contributions. There is a poster produced by the Boehringer Mannheim company that details every chemical reaction in a 'typical' cell, the poster details all of the pathways, enzymes and products necessary for life. It is an impressive visual statement about the entire process, and I suspect you would be able to e-mail them to obtain a set (Biocehmical and Molecular) for your classroom. In the Internet age, a collection of metabolic pathways and their links has been put together by a group in Japan, called the Kegg, and it performs a similar function, but it better linked, provides references, and will show you other pathways in which a protein/enzyme is involved.

As for the major determination of the metabolic products, most of this work was performed by the analysis of mutations in organisms at particular steps in the process and essentially seeing what product accumulated. Likewise, it is possible to quantitate the amount of ATP produced from NADH+H+ using similar methods. Of course, Hans Krebs was instrumental in determining many aspects of metabolism, and the TCA cycle bears his name as a result. For his work, he recieved a Nobel Prize.

Beginning with glycolysis, (The conversion of sugar into ethanol, lactic acid, acetate, pyruvate etc.) it was demonstrated by Louis Pasteur in 1854-64 that fermentation was caused by microorgansism. in 1897 Edward Buchner illustrated that cell-free yeast extracts were also able to perform this process. The dissection of the glycolytic pathway was performed primarily by three individuals, Otto Meyerhof, Javob Parnas and Gustav Embden, which is why glycolysis is also known as the Embden-Meyerhof - Parnas pathway. Other contributors were Carl nad Gerti Cori Carl Nerberg, Robert Robison and Otto Warburg.

Of course, the products from glycolysis, NADH+H+, and pyruvate are funneled into the citric acid cycle to generate more NADH+H+ (reduced), which is coupled to the synthesis of ATP. I will describe the individuals responsible for that now.

It has long been known that organisms oxidize carbon sources, such as glucose to CO2 and water. After the advent of enzymology, it was possible to elucidate the mechanisms by which this process generates energy (ATP). Otto Warberg established that biological oxidations are catalyzed by enzymes. Lehninger and Kennedy discovered that the mitochondria contained the enzymes that mediate the process of electron transport. The primary workings of the electron transport chain were determined through the use of inhibitors, of which many were found to act at specific steps. Cynaide, for example, is a potent inhibitor of electron transport. It acts by inhibiting electron transport at all three donors, indicating that it blocks the electron- transport chain after the third point of entry.

The function of the cytochromes, essential for electron transpoirt was elucidated by David Keilin. The chemiosmotic hypothesis. Proposed by Peter Mitchell is idea that the free energy of the electron transport is coupled by the pumping of protons across the mitochondrial or bacterial membrane. The proton gradient is what drives the synthesis of ATP.

The Nobel Prize in 1997 was given to three individuals who determined the mechanism of ATP synthesis, John Walker, and Paul Boyer. There are dozens more individuals involved in the determination of various aspects of this extremely diverse and dynamic process, and I hope this brief review is of some assistance. Thanks for the question.

-Matt-

References: Voet & Voet Biochemistry Second Edition 1995

Nobel web site http://www.nobel.se