What is the Difference Between Calmodulin and Troponin C?

Calmodulin and troponin C are both calcium-binding proteins found in eukaryotes, but they have distinct functions and structures. Here are the main differences between them:

1. Location: Calmodulin is present in the cytoplasm of all eukaryotic cells, while troponin C is found in cardiac and skeletal muscles.
2. Function: Calmodulin mediates calcium-dependent signaling, while troponin C regulates muscular contraction.
3. Structure: Troponin C is a complex of three proteins, while calmodulin is composed of two globular domains connected by a central alpha-helix.
4. Calcium-binding: Both calmodulin and troponin C have four EF-hand motifs that can bind calcium (and/or magnesium) ions. However, calmodulin can bind only with calcium, whereas troponin C can bind with both calcium and magnesium.
5. Activation: In the presence of 10 microM free Ca2+, the troponin C-activated ATPase reaches a maximal velocity of approximately 70% of that attained with calmodulin. The half-maximal concentration for troponin C activation is about 200 times greater than for calmodulin.

In summary, calmodulin and troponin C are both calcium-binding proteins with different functions, structures, and calcium-binding properties. Calmodulin is involved in calcium-dependent signaling, while troponin C regulates muscular contraction.

Comparative Table: Calmodulin vs Troponin C

Here is a table comparing the differences between calmodulin and troponin C:

Please note that the EF-hand motifs in calmodulin can bind to calcium and/or magnesium ions, while troponin C can bind to both calcium and magnesium ions.