Definition check in enzymology: What is the functional role of a kinase enzyme in metabolism?

Introduction / Context:
Kinases are ubiquitous regulatory enzymes in biochemistry, central to signal transduction and metabolic control. Recognizing their precise catalytic role is essential for interpreting pathways such as glycolysis, glycogen metabolism, and phosphorylation cascades.

Given Data / Assumptions:

• ATP commonly serves as the phosphate donor in kinase reactions.
• Phosphorylation can modulate enzyme activity, protein–protein interactions, localization, or stability.
• Phosphatases counteract kinases by removing phosphate groups.

Concept / Approach:
A kinase catalyzes transfer of the terminal phosphate (often the gamma phosphate) from ATP to an acceptor substrate (e.g., a hydroxyl group on serine, threonine, tyrosine in proteins, or small metabolites such as glucose). This post-translational modification or metabolite activation underlies many on/off switches in cellular regulation.

Step-by-Step Solution:
Identify the canonical reaction: Substrate–OH + ATP → Substrate–O–PO3 + ADP.Distinguish from phosphatase (reverse reaction: dephosphorylation).Exclude oxidoreductase activity (NADH/NAD+), lyase/dehydratase functions, or acyl transfer.Select the definition that matches phosphorylation using ATP: option (b).

Verification / Alternative check:
Textbook examples include hexokinase (glucose → glucose-6-phosphate) and protein kinases (PKA, PKC, MAPKs) that regulate signaling pathways by phosphorylating target proteins.

Why Other Options Are Wrong:

• Removes phosphate groups: That is a phosphatase.
• Uses NADH: Oxidoreductases perform redox, not phosphorylation.
• Removes water: Dehydratases/lyases, not kinases.
• Acyl transfers: Acyltransferases or transacylases handle acyl groups, not phosphate transfer from ATP.

Common Pitfalls:
Confusing kinases (add phosphate) with phosphatases (remove phosphate); always check the direction of phosphate movement and ATP involvement.

Final Answer:
Uses ATP to add a phosphate group to a substrate (phosphorylation).