Actin and Myosin

ID #1568

I was just wondering if anyone could clarify something for me. When we were talking about actin binding proteins, did we say that the more G actin they hide, the critical concentration drops and therefore it depolymerizes? But I was thinking that if more G actin were hidden, it would polymerize more...

Yes, we did say that if more G-actin is "hidden" by ABPs, this would (probably) favor depolymerization. Let's look at why. Depolymerization is favored if you are below the critical concentration, Cc. And the Cc in turn is the amount of available G-actin necessary to be at steady state. Hiding G-actin by binding another protein to it effectively lowers the concentration of available G-actin, and as soon as you get below the Cc, you'll start to depolymerize. Technically, if your amount of available G-actin to begin with was really high, hiding some of it still might not even get your level down to the Cc, or perhaps right at the Cc, so you don't automatically have to be depolymerizing just because more G-actin is hidden, but the point I'm making is that you'll never be inducing polymerization by taking G-actin out of the population.

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