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.

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

Are the genes encoding the proteolytic enzymes expressed in the same cell types in all species?
Once the precursor proteins of different species are cleaved, do the active signaling proteins bind to the same receptors on different target cells?
If a proteolytic enzyme from one species is incubated with a precursor protein from another species, does correct cleavage occur?
Are the proteolytic enzymes synthesized in the rough endoplasmic reticulum of all species?