Some cells release active signaling proteins when membrane-bound precursor proteins are cleaved by proteolytic enzymes. The signaling proteins can then bind to receptors on the surface of a target cell, thereby activating an intracellular signaling pathway and eliciting a response from the target cell.

This mechanism of activating receptor-binding signaling proteins has been observed in a variety of organisms from bacteria to humans. Many of the enzymes responsible for proteolysis of membrane-bound precursor proteins have been isolated and characterized.

Which of the following questions would be most appropriate to investigate whether the proteolytic enzymes are evolutionarily conserved among species?

If the proteolytic enzyme is evolutionarily conserved, it should have a similar function across species. We can test this out by seeing if the enzyme functions accordingly in different species.

Checking if the genes of the enzymes are in the same cell types wouldn't be as appropriate since this could simply occur due to convergence. Similar cell types may require a function that only a certain enzyme structure could fulfill.

Asking about the products of cleavage doesn't give us any information about the enzyme.

Many proteins are synthesized in the rough endoplasmic reticulum, so it may be just a coincidence to see similarities among enzymes from different species.