The Stopped-flow Method and Chemical Intermediates in Enzyme Reactions - A Personal Essay

My perspective does not deal directly with photosynthesis research. However, the methods evolved have played an important role in several areas of biochemistry and biophysics including photosynthesis. Improvements of rapid reaction methods, based upon the pioneering studies of Hamilton Hartridge and F.J.W. Roughton, and Glenn Millikan, required a detailed study of the hydraulics of small-bore tubes and jet mixers, taking into account, that economy of reactants was demanded by the sparcity of enzyme preparations in the 1930s. This Personal perspective recites the steps taken to minimize the volumes expended in rapid flow studies, together with the improvements in electronic technology of rapid and sensitive spectrophotometry of labile intermediates in enzyme reactions. Of the methods studied, continuous, accelerated and stopped flow, the latter was designed for the highest fluid economy and subsequently proved to be of wide use for studying biochemical kinetics. Advances in fast spectrophotometry of dilute solutions led to great improvements in Millikan's dual-wavelength system, both in speed of recording and decreases of background noise level, largely due to electronic stabilization of light sources and sensitive amplifiers. The application of these technologies to studies of hemoglobin, myoglobin and heme enzymes was, more recently, followed by studies of suspensions of organelles, cells, and tissues not only in vivo but also at low temperatures with cryoprotectants, leading to the use of flash activation in carbon monoxide inhibited heme enzymes. Laser technology allowed photosynthetic systems to be studied at cryotemperatures, leading to the development of electron tunneling theories for biological reactions (not discussed in this paper). All in all, the many fundamental developments of electronics, optics and hydraulics indicate how technology can respond effectively to the needs of biology in general, and photobiology in particular.