<title>Fluorescence intensity and anisotropy decays of the intrinsic tryptophan emission of hemoglobin measured with a 10-GHz fluorometer using front-face geometry on free liquid surface</title>

Abstract

We measure the intensity and anisotropy decays of the intrinsic tryptophan emission from hemoglobin solutions obtained using a 10 GHz frequency-domain fluorometer and a specially designed cuvette which allows front face excitation on a free liquid surface. The cuvette eliminates reflections and stray emissions, which become significant for low intensity fluorescence like in hemoglobin. Three lifetimes are detectable in the subnanosecond range. The average lifetime of hemoglobin is ligand dependent. Fluorescence anisotropy decays of oxy, deoxy, and carbonmonoxyhemoglobin can be fitted with up to three correlation times. When three components are used the floating initial anisotropy r<SUB>o</SUB> is in each case higher than the steady-state anisotropy of tryptophan in vitrified solution. For deoxy hemoglobin it is close to 0.4. The data are consistent with an initial loss of anisotropy from 0.4 to about 0.2 occurring in the first two picoseconds.