Most proteins in the cell are not produced “ready to go”. Instead, they are first synthesized with chains of amino acids that block their activity until they are removed by enzymes called “proprotein convertases” (PCs). This family of enzymes plays significant but very different roles in various cancers, and regulating the activity of PCs could help develop cancer treatments. But PCs overlap in terms of activity, meaning that two or more of these enzymes can process the same protein. This overlap makes it very difficult to distinguish and map out the functional profile of each PC.