Cellular actin levels can be as high as 100-400 µM. Of this, unpolymerized actin concentration can be as much as 50-200 µM. However, the critical concentration for actin polymerization in-vitro is about 0.2 µM. Some of the following proteins inhibit polymerization of actin in cells:

A. Thymosin-β₄
B. Capping protein CapZ
C. Tropomodulin
D. XMAP215

Which one of the following options lists all inhibitors?

Correct option is A

Explanation-

​A. Thymosin-β4
Thymosin-β4 inhibits polymerization. It binds G-actin monomers and prevents them from polymerizing into F-actin.
B. Capping protein CapZ
Capping protein CapZ inhibits polymerization. It binds to the plus end of actin filaments, preventing the addition of new monomers.
C. Tropomodulin
Tropomodulin inhibits polymerization. It binds to the minus end of actin filaments, stabilizing them and preventing elongation or depolymerization.
D. XMAP215
XMAP215 does NOT inhibit actin polymerization. It is a microtubule polymerase, not related to actin. It promotes microtubule growth.

Correct answer: Option a: A, B, and C only