A Fixable Fluorescence‐Quenched Substrate for Quantitation of Lysosomal Glucocerebrosidase Activity in Both Live and Fixed Cells

Abstract Fluorogenic substrates are emerging tools that enable studying enzymatic processes within their native cellular environments. However, fluorogenic substrates that function within live cells are generally incompatible with cellular fixation, preventing their tandem application with fundamental cell biology methods such as immunocytochemistry. Here we report a simple approach to enable the chemical fixation of a dark‐to‐light substrate, LysoFix‐GBA, which enables quantification of glucocerebrosidase (GCase) activity in both live and fixed cells. LysoFix‐GBA enables measuring responses to both chemical and genetic perturbations to lysosomal GCase activity. Further, LysoFix‐GBA permits simple multiplexed co‐localization studies of GCase activity with subcellular protein markers. This tool will aid studying the role of GCase activity in Parkinson's Disease, creating new therapeutic approaches targeting the GCase pathway. This approach also lays the foundation for an approach to create fixable substrates for other lysosomal enzymes.