Napththylamine sulphonic acids are often used as extrinsic labels for proteins. One useful derivative is 2-diethylamino-5-napthalenesulphonic acid (DENS) which has a relatively long fluorescence lifetime of ~30 ns. A) Give a brief description of the principles of fluorescence anisotropy, illustrating your answer with appropriate diagrams and equations B) Suppose the fundamental anisotropy of DENS is 0.30 and that DENS is bound to a protein with a rotational correlation time of 30 ns. What is the anisotropy? C) Assume now that the protein is bound to an anti-body with a molecular weight of 160,000 and a rotational correlation time of 100 ns. What is the anisotropy of the DENS-labeled protein?

Napththylamine sulphonic acids are often used as extrinsic labels for proteins. One useful derivative is 2-diethylamino-5-napthalenesulphonic acid (DENS) which has a relatively long fluorescence lifetime of ~30 ns. A) Give a brief description of the principles of fluorescence anisotropy, illustrating your answer with appropriate diagrams and equations B) Suppose the fundamental anisotropy of DENS is 0.30 and that DENS is bound to a protein with a rotational correlation time of 30 ns. What is the anisotropy? C) Assume now that the protein is bound to an anti-body with a molecular weight of 160,000 and a rotational correlation time of 100 ns. What is the anisotropy of the DENS-labeled protein?