Cathepsin A is active in cellular compartments called lysosomes. These compartments contain enzymes that digest and recycle materials when they are no longer needed. Cathepsin A interacts with the enzymes β-galactosidase and neuraminidase 1, which play a role in the breakdown of complexes of sugar molecules (oligosaccharides) attached to certain proteins (glycoproteins) or fats (glycolipids). Cathepsin A forms a complex with these two enzymes and directs their transport within the cell to the lysosomes. Within lysosomes, cathepsin A activates the enzymes and prevents their breakdown.

> 95% as determined by SDS-PAGE.