Selective laser-induced inactivation of proteins (SLIP) by labelling with chromophores

Coupling a fluorochrome (e.g. fluorescein-isothiocyanate, FITC) to a molecule can enhance specific laser light absorption, thus leading to alteration or even destruction of the molecule itself. Therefore antibodies were labelled with FITC (absorption maximum 480 nm) and irradiated with laser light (488 nm) under various conditions. Inactivation of antibodies could only be achieved at the absorption maximum of FITC (as measured by direct and indirect immunofluorescence). Positive linear correlation exists between the amount of destruction and both exposure time and energy. Similar destructive effects were obtained when FITC-labelled peroxidase was irradiated. In these cases, enzyme activities measured by absorption photometry also showed a positive correlation to the total amount of energy transferred. Non-labelled proteins were not affected by irradiation. So we conclude that labelling of proteins with fluorochromes provides a highly specific means of selection of target molecules to be destroyed or inactivated. The method is based upon the laws of linear optics and is different from photodynamic or photochemical actions. The destructions observed are most likely caused by thermally induced changes of the molecules' tertiary structure.