Terminology check: what is the name for the inactive protein form of an enzyme (lacking its required cofactor or coenzyme)?

Introduction / Context:
In enzymology, precise terminology avoids confusion when designing assays or reading literature. Enzymes can exist in a protein-only form or as a fully assembled, active complex. The inactive protein portion has a specific name that appears frequently in protocols.

Given Data / Assumptions:

• We are asked about the inactive protein form.
• The absence of the cofactor/coenzyme is implied.
• We must choose the correct term among common but easily confused names.

Concept / Approach:
The apoenzyme is the protein portion lacking required non-protein components. When the apoenzyme binds its cofactor or coenzyme, it becomes a holoenzyme (note: sometimes misspelled as “haloenzyme”). A cofactor is the non-protein helper itself, not the protein.

Step-by-Step Solution:

Verification / Alternative check:
Biochemistry references define apoenzyme + cofactor = holoenzyme, confirming the nomenclature.

Why Other Options Are Wrong:

• Enzyme: generic term, not specific to the inactive protein portion.
• Haloenzyme (misspelling): intended “holoenzyme,” which is active, not inactive.
• Cofactor: non-protein component, not the protein itself.

Common Pitfalls:
Spelling mistakes (“haloenzyme”) or mixing up “cofactor” and “coenzyme” with the protein portion.

Final Answer:
apoenzyme