Exploring Light and Life

Theinterplay of light and life has fascinated me since my college years. In the introductory biology laboratory at the University of Chicago, we isolated chloroplasts and carried out the Hill reaction, in which light leads to the reduction of an indicator dye with the concomitant generation of O2. I vividly recall my excitement on seeing this graphic demonstration of key features of photosynthesis in a test tube. Equally important weremy evenings as awaiter at theQuadrangle Club, where I had the good fortune of serving James Franck, a distinguished emeritus professor of chemistry who had received the Nobel Prize in 1925 for carrying out experiments that established the validity of Bohr’s model of the atom. My task was simple because he invariably ordered a lean veal sandwich for dinner, and so there was time for conversation. Franck told me about his current interest in the mechanism of photosynthesis and his early research on energy transfer. In 1923, Franck and his graduate student Günther Cario reported that excitation of mercury led to the emission of thallium in a gaseousmixture of the two atoms (1). This sensitized fluorescence revealed that electronic excitation energy can be transferred between atoms by a direct electromagnetic interaction. Later in the quarter, Franck remarked to me, “One day, you too might work on energy transfer.” That day came two years later, in 1957, when I spent a very rewarding summer as a research student at the Argonne National Laboratory under the mentorship of Douglas Smith. He introduced me to photodynamic action, a process in which light activates a photosensitizing dye in the presence of O2 to induce cellular damage, and encouraged me to read about energy transfer because it often plays a key role in effecting the light-induced damage. I learned that energy transfer can take place between any two chromophores provided that the emission spectrum of the energy donor overlaps the absorption spectrum of the energy acceptor. I was captivated by Theodor Förster’s theory for dipole-dipole energy transfer, which explicitly predicted the rate and efficiency of transfer as a function of spectroscopic and geometric variables (2). What especially grabbed me was his prediction that the transfer efficiency depends on the inverse sixth power of the distance between the donor and acceptor. During that summer and the following one, I learned how to carry out fluorescence measurements and label proteins. My first published paper dealt with energy transfer from aromatic amino acids in chymotrypsinogen to attached dansyl groups (3). At a bioenergetics meeting at Brookhaven in 1959, where I met Förster, I reviewed the literature on energy transfer in proteins and suggested that energy transfer could be used as a probe to gain insight into the conformation of biological macromolecules (4). A highlight of that year was visiting Franck to let him know that I was indeed working on energy transfer. As a medical student at Harvard University, I carried out research under the mentorship of Elkan Blout, who was Director of Chemical Research at Polaroid by day and head of a basic research laboratory at Children’s Hospital by night. At Polaroid, Elkan worked closely with Edwin Land in developing instant color photography, and at Harvard, he synthesized synthetic polypeptides as models of proteins and studied their conformations using spectroscopic techniques. I wanted to find out how dyes bound to synthetic polypeptides altered their conformation and began bymonitoring the known helix-coil transitions of poly-L-glutamic acid and poly-L-lysine by THE JOURNAL OF BIOLOGICAL CHEMISTRY VOL. 287, NO. 19, pp. 15164 –15173, May 4, 2012 Author’s Choice © 2012 by The American Society for Biochemistry and Molecular Biology, Inc. Published in the U.S.A.