Cathepsin D assay to verify the retention of lysosomal content v1

Cathepsin D assay is a fluorescence-based assay that leverage on the activity of cathepsin D, a lysosomal enzyme, to monitor the intactness of lysosome in the cell. Here, we describe a method where we used the measurement of cathepsin D activity to verify the intactness of lysosomes that were isolated from HEK293 cells based on anti-TMEM192 Lyso-IP. Our data showed an increase in the cathepsin D activity of lysosomal fraction when compared with whole cell fraction and Mock-IP fraction, an indication that the lysosomes are intact and viable.