When enzymes are exposed to extreme pH's what makes them denature?

Question

How does pH effect amino acid structure

How does pH effect the ionization of amino acid side chains

Answer 1

You answered your question by yourself; The structure of proteins depends partly on ionic bonds and H-bonds that are formed by the groups of the side chains of the amino acids.
Changing the pH will change the ionisation of the groups and thus under certain conditions they will not be able to participate in the same bonds as before. Breaking these bonds leads to a loss of structure and consequently loss of function.

Let's take for example aspartate.
The side-chain is -CH2-COOH with pKa=4.0
This means that at physiological pH (which is neutral;pH=7) the equilibrium
-CH2-COOH <=> -CH2-COO- + H+
is shifted to the right so that practically asp residues are in the negatively charged state. In this state Asp can form an ionic bond with a positively charged side chain like that of Lys or Arg.
If you go at pH
Similarly for positively charged side chains, when you go to pH>pKa you lose the positve charge.

Also if you consider tyrosine, which has side chain -CH2-C6H4-OH and pKa=9.84 at pH=7 it will be protonated and the H will be able to take part in H-bonds both as a donor (through H) and an acceptor (through O) At pH>pKa the side chain will be deprotonated (-CH2-C6H4-O-) so it will be able to act only as an acceptor.

at http://en.wikipedia.org/wiki/Protein_pKa_calculations
you can see which amino acids can have charged side chains and their pKa.

Answer 2

Enzymes are proteins and proteins are polymers made up of chains of monomers known as amino acid. Proteins also have different level of structures which are maintain by different types of bondings. These include primary,secondary and tertiary structure. Due to the structure of an amino acid, which has both the COO group and the NH3(-) groups, it has both acidic and basic properties and is said to be amphoteric. These properties makes the protein sensitive to changes in the H+ ion concentration and hence, either extreme pHs would cause the protein to lose its secondary and tertiary structure which are necessary to maintain its specific shape and structure. When acids are being added as H+, they combine with the COO groups on amino acids at active sites to form CO-OH, therefore, the specific shape of the enzyme is being lost and it is said to be denatured. In basic conditions, the reduce number of H+ ions causes the NH3(-) group on the amino acid to lose its H+ ions, forming NH2. Similarly, the enzymes loses its specificity and it is said to be denatured.

Answer 3

Enzymes are specific as to what pH they work at. However strong acid will denature a protein, and enzymes are proteins. Try putting strong acid on egg white and watch it turn white like a cooked egg white which is denatured.The acid makes the amino acids become less soluble because of cross bonds,

Answer 4

Each enzyme has an optimal pH that helps maintain its three-dimensional shape. Changes in pH may denature enzymes by altering the enzyme's charge. This alters the ionic bonds of the enzyme that contribute to its functional shape.


At pH lower than7.0 i.e. acidic conditions ,nitrogen develops positive charge.
At pH higher than7.0 i.e. basic conditions ,the carboxylic group loses the proton and hence becomes negatively charged.
Each amino acid has a particular pH at which no charge develops known as the "isoelectric point"

Answer 5

enzymes are primarily protein chains. One of the major factors in a prtein folding in to a specific form is hydrogen bonding between N-H C=O and O-H groups. changing the pH adds or removes H+ ions which can perturb this and cause the protein to lose its shape.

Answer 6

depends on which enzyme ...like amylase enzyme works best on pH7...when the pH is way higher or lower than ph7..it will not work properly...pepsin works best on pH2.5 while tripsin on pH8.0...

Answer 7

in our breadbasket where pH is 2