Roughly 100,000 different proteins function as the workhorses of the human brain. They act as chemical agents, delivering and receiving neural messages, and help to construct or reconstruct neural pathways. Understanding how these subcellular components function could assist in the discovery of new drug therapies or cast new light on functional genomics. Chromophore-assisted laser inactivation uses laser energy to arrest the activity of specific proteins within a cell structure to learn more about what functions those proteins serve. One approach to better understanding proteins uses chromophore-assisted laser inactivation. Pioneered by Dan Jay, an associate professor of physiology at Tufts University School of Medicine, this technique uses laser pulses to inactivate specific proteins tagged by chromophores. More specifically, Jay's lab applies the technique to study the proteins that guide axon growth and nerve regeneration. Essentially, Jay inactivates a protein in a specific cell or embryo with an antibody labeled by a chromophore -- malachite green dye, which absorbs 630-nm light. Thus, pulses from a nitrogen-pumped dye laser excite the chromophore, causing it to release short-lived free radicals that arrest the function of the antibody-bound protein. In its earlier form, chromophore-assisted laser inactivation relied on a 2-mm spot from a doubled Nd:YAG. Although he still uses the YAG, he has added to his lab a nitrogen-pumped dye laser from Laser Science Inc. to help refine the technique. In the refined micro version, Jay is able to focus the laser beam into a 10-µm spot to localize protein inactivation within select portions of a cell. "This gives us the ability to generate acute and localized loss of a protein's function during a cellular process," he said. "If we understand what a protein does or how it's involved in disease, then that protein becomes a good candidate to target drug development." Cost was the main driver in Jay's selection of the dye laser, which he said runs about a tenth of the price for standard Nd:YAG instruments. In addition, Laser Science's pulsed dye laser provided the right photon flux -- the balance of intensity and power -- to perform Jay's refined method. The laser also delivers the 30-mW/cm2 peak power density called for in this application.