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?

Question

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?

BlackTom AI · Accepted Answer

To tackle this question, I’ll evaluate what it means for proteolytic enzymes to be evolutionarily conserved and how we would test that.
Option 1: Are the proteolytic enzymes synthesized in the rough endoplasmic reticulum of all species?
This question focuses on cellular localization and biosynthetic compartments, not on whether the enzymes are evolutionarily conserved across species. Proteolytic enzymes can be synthesized in different cellular contexts in various organisms, so this does not directly test evolutionary conservation of the enzymes themselves. It may be informative for cell biology, but not for conservation across species in terms of function.
Option 2: Are the genes encoding the proteolytic enzymes expressed in the same cell types in all species?
Expression patterns reveal regulatory conservation, not necessarily structural or catalytic conservation of the enzymes. Even if expression differs, the enzymes could still be evolutionarily conserved in sequence and function. Therefore, this question addresses regulation rather than the biochemical conservation of the enzymes across species.
Option 3: Once the precursor proteins of different species are cleaved, do the active signaling proteins bind to the same receptors on different target cells?
This question examines whether the downstream signaling outcomes are conserved after cleavage, which relates to target receptor compatibility and signaling pathways. It tests functional consequences in recipients, not the conservation of the proteolytic enzymes themselves. The focus is downstream compatibility rather than whether the enzymes are conserved across species.
Option 4: If a proteolytic enzyme from one species is incubated with a precursor protein from another species, does correct cleavage occur?
This directly tests the biochemical compatibility between an enzyme and a substrate across species, which is a strong indicator of structural and functional conservation of the proteolytic enzymes themselves. If correct cleavage happens, it suggests the enzyme’s catalytic mechanism is preserved across species; if not, divergence is evident. This approach directly probes evolutionary conservation of the enzyme’s activity across species.
In summary, options 2 and 3 shift attention away from enzyme conservation toward regulation or downstream signaling rather than the core question of whether the proteolytic enzymes themselves are conserved. Option 1 focuses on cellular localization rather than cross-species enzymatic similarity. Option 4 directly assesses cross-species enzymatic compatibility, making it the most appropriate test for evolutionary conservation of the proteolytic enzymes across species.

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