Enzyme activity - salinity, SH bonds

[yestomeds]

1) How does salinity changes within the body affect the hydrogen bonds of the enzyme? (paraphrasing something from Kaplan).

2) HS-SH (disulfide covalent bridges) - in what cases in the body (or i guess in any location) would they be prone to be disrupted?

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[Quinoline]

1. More salt may cause the H bonding structures to associate around the ion.
Low salt can help proteins dissolve by stabilizing charges on the protein.
Too much salt can cause proteins to precipitate by attracting all of the water so the protein isn't dissolved.

2. In reducing environments like cytoplasm, disulfide bonds can break, as the S get reduced -S-S- -> -SH HS-

 

[basophilic]

1. More salt may cause the H bonding structures to associate around the ion.
Low salt can help proteins dissolve by stabilizing charges on the protein.
Too much salt can cause proteins to precipitate by attracting all of the water so the protein isn't dissolved.
View attachment 193402

2. In reducing environments like cytoplasm, disulfide bonds can break, as the S get reduced -S-S- -> -SH HS-

For 1, so high salt concentrations can disrupt secondary as well as tertiary and higher structures?
Also, how come lower pH (but high enough to prevent nonspecific hydrolysis) can disrupt only electrostatic interactions but not H-bonds (and hence only tertiary and higher but not secondary structures, according to Khan denaturation video), but a salt can disrupt H-bonds?

 

[Quinoline]

Hydrogen bonds rely on protonated sites. At mildly low pH, these sites will be protonated so the interactions will be fine. Electrostatic interactions are between a positively and negatively charged group. At low pH, the negatively charged group may become protonated and no longer negative, breaking the interaction. COO- -> COOH

 

[yestomeds]

2. In reducing environments like cytoplasm, disulfide bonds can break, as the S get reduced -S-S- -> -SH HS-

Thanks @Quinoline! So you're saying that inside the cell (cytoplasm), the bonds are oxidized. Because they are oxidized, they break.
So SH-SH bonds are in the reduced forms, therefore, they would not be found within a cell? How does that impact or how does it have something to do with aa or protein function (wrt our human cells, or bodies?).

Hope my follow up questions make sense!

 

[Quinoline]

Actually it is the other way around. Inside the cell, the disulfide bonds are reduced and broken. Like you said, -SH HS- is the reduced form and is also when the bond is broken. The oxidized form -S-S- is when the bond is formed.

The amino acid cysteine can make disulfide bonds with other cysteines. The structure and function of a protein may change depending on if the disulfide bonds are formed are not. For example, a protein may be made inside a cell, but it does not work inside the cell because its disulfide bonds are broken. Once the protein gets exported outside of the cell, it can then be functional because the disulfide bonds form.