GFP Chromophore (image) University of California - Berkeley Caption After GFP's chromophore absorbs a blue photon, its excited phenoxyl-ring wags rapidly back and forth, settling into a position that allows a negatively charged hydrogen atom -- a bare proton -- to hop along the dotted lines, leading to bright green fluorescence. The red balls are oxygen atoms, the small silver balls are hydrogen atoms (protons), the large silver balls are carbon atoms, and the blue balls are nitrogen. The green background is the barrel-like structure of GFP, which encloses the central chromophore. Credit Renee Frontiera & Chong Fang/UC Berkeley Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.