Cytochemical localization of ornithine decarboxylase with rhodamine or biotin-labeled alpha-difluoromethylornithine. An example for the use of labeled irreversible enzyme inhibitors as cytochemical markers.

The present work describes a new method for cytochemical localization of enzymes using ornithine decarboxylase (ODC) as an example. The method is based on the preservation of the characteristic-specific and irreversible binding of the inhibitor alpha-difluoromethylornithine (alpha-DFMO) following its conjugation to "label" molecules. The inhibitor has been conjugated to the fluorescent molecule rhodamine-B-isothiocyanate, and its localization in tissue sections was detected directly by fluorescence cytochemistry. Alternatively, alpha-DFMO has been conjugated to biotin and its cytochemical localization determined indirectly following its binding with avidin conjugated to horseradish peroxidase (HRP) and visualization of the HRP reaction product. Both labeled inhibitor molecules were successfully localized cytochemically within specific cells of the developing rat cerebellum and rat liver following thioacetamide injection where ODC activity is greatly enhanced. This novel technique should be of general application 1) in other tissues, 2) for other enzymes, and 3) in electron microscopic studies for ultrastructural localization of the enzyme.