My first graduate student, Woonsup Shin, and I set up the lab in 1989, including a glove box, EPR spectrometer, and other equipment required for growing bacteria and purifying the nickel-containing exquisitely air-sensitive enzyme acetyl-CoA synthase/carbon monoxide dehydrogenase (ACS/CODH). Little was known about the role of nickel in biology at the time and my goal was to figure out why this enzyme contained nickel. The number of metal sites and the role of each site were largely unknown. I wanted to perform electrochemical titrations inside of a glove box and correlate those changes with changes in EPR and Mössbauer spectra (the latter technique was done collaboratively with Eckard Münck at Carnegie Mellon University). Then, in about 1991, Woonsup accidently discovered that a portion of the Ni could be removed from the enzyme, and that this had a very specific effect on activity and spectroscopic properties. We shifted gears and "milked" that discovery for all it was worth. We were able to determine the number and function of active sites, and probe the mechanism of catalysis as never before. In hindsight, without this discovery, I probably would never have gotten tenure! Thanks Woon! I should mention that in about 1990 I started a second project involving Ni-containing hydrogenases, and we did similar types of studies (redox titrations monitored by EPR). Despite publishing a couple of good papers on hydrogenase, I never obtained funding for these studies, so I eventually dropped the project. On the other hand, I expanded my studies on ACS/CODH to include stopped-flow kinetics, site-directed mutagenesis, and protein crystallography. I focused on this bifunctional enzyme exclusively for many years, and like to think that I made some significant contributions to this field.
In 1997, I noticed a paper by Gunter Wächtershäuser in which "my enzyme" was implicated in the origin of life (fixing CO2 on a Ni/Fe/S surface). I became enthused with this idea, and especially with the concept of autocatalysis. I almost began an origin-of-life research project, but realized at the last minute that my interest was actually more in describing life from a chemical perspective rather than in trying to figure out exactly how it started. These ideas dovetailed with the developments in genome sequencing and systems biology that were being made at the time. I thought: if we only know what each gene of an organism did, we could understand life! In 2000, I began to collaborate with Jeff Morgan, now Professor of Mathematics at the University of Houston. After going around in circles for about 5 years, we eventually developed a viable computational research program on Whole Cell Mathematical Modeling.
Meanwhile it became increasingly difficult to entice new graduate students to work on ACS/CODH, as attitudes had shifted. Why study an enzyme that does not cause or cure any disease, they asked? Responding that the chemistry was interesting simply wasn't enough. I wondered what I could do experimentally in which I could use my skills (anaerobic bioinorganic chemistry and biophysical spectroscopy) that could impact human health?
In 2004, I happen to read an article by Roland Lill (Philips University, Marburg Germany) in which he mentioned that the matrix of mitochondria was essentially anaerobic. Indeed, this is the primary location of Fe/S cluster assembly, and the enzymes involved are O2-sensitive. Given my glove-box experience, I felt that I could contribute somehow to this field. So I combined these thoughts and my background with my recent dabblings in computational systems biology and decided to study iron metabolism, not at the level of individual proteins, but from 36,000 feet. I recruited a new graduate student, Brandon Hudder, for this project. Brandon was a synthetic inorganic chemist who had no background in biochemistry much less cell biology. He did, however, have courage and was quite adventurous. I decided to focus on Mössbauer spectroscopy, as it would allow us to "see" all of the iron in any sample, no matter how complicated. We had no idea what we would see when we ran the first Mössbauer spectrum of isolated mitochondria. The good news was that, although we could not distinguish individual Fe-containing proteins, we could see groups of Fe species that appear to be involved in Fe trafficking which is sort of a trendy new field. Since then, we have expanded our interests to vacuoles, whole cells, and most recently mice. I'm also moving into metallomics, but don't have anything substantive to say at this point. That's where we are at in 2011. Stay tuned...