protein folding enthalpy

[theonlytycrane]

Going from a non-folded protein to a folded protein, would enthalpy change be negative (energy released)? I was thinking that it would take energy to break interactions (ionic, hydrophobic, and van der Waals) in the folded protein to get back to the non-folded state so going in the reverse would release energy.

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[David513]

I can't speak to enthalpy but in my biochemistry course we just discussed why protein folding is a spontaneous process. This is because, although entropy decreases going from a non-folded to folded protein since you are going from a less ordered to a more ordered state (-∆S), you allow the water molecules in the environment to remain highly disordered/with a higher entropy (+∆S) because you are moving hydrophobic side chains away from water and hydrophilic side chains toward water. This yields a net increase in entropy for the entire folding process and, thus, a negative free energy (-∆G), i.e. it's a spontaneous process due to the ∆G=∆H-T∆S law.

I know that didn't discuss enthalpy but I think it addresses your question still...!

 

[vivatix]

When a protein is folded, bonds are created and we know that when bonds form, water is lost (dehydration synthesis) and energy is released. Energy is this case refers to gibbs free energy - meaning that unfolded proteins will fold and form interactions (in the right environmental conditions - temperature, pH etc) and these folded proteins are more stable than the unfolded state - i.e folding process is spontaneous.

So, using the ∆G=∆H-T∆S law, we know that ∆G is negative and ∆S is negative - we can determine that ∆H would also have to be negative and the process will be exothermic.

Keep in mind that when you are thinking of bonds breaking (energy and water are added to break bonds) and bonds forming (energy and water being released), energy is referring to ∆G. But overall, the breaking of bonds is a spontaneous (negative ∆G) process because more energy is released when you break the bonds than the amount of energy you need to put in. For example, glycolysis.