Excited state proton transfer (ESPT) of pyranine (8-hydroxypyrene-1,3,6-trisulfonate) is studied in a lysozyme-cetyltrimethylammonium bromide (CTAB) complex using picosecond emission spectroscopy. The critical association concentration (CAC) of CTAB is found to be similar to 0.4 mM. Using a kinetic analysis it is shown that deprotonation, recombination and dissociation of the geminate ion pair in the lysozyme-CTAB aggregate are faster than that in a CTAB micelle. (c) 2005 Elsevier B.V. All rights reserved.