Did you look in the Sigma catalog? There are a lot there. p-nitroanilide derivatives are good. rich -- --- --- --- -- -- -- --- --- --- Richard J. Dudley (rdudley+ at pitt.edu) Research Specialist V Dept. of Cell Biology and Physiology University of Pittsburgh http://www.cbp.pitt.edu ---> search BIONET archives at http://www.bio.net <---