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You mean "why is a protein least soluble when the pH of aqueous media matches the value of its isoelectric point?".
The answer is that at its isoelectric point the protein surface carries no net charge. As protein solubility is based upon favourable electrostatic interactions between the charges (negative or positive) on the protein surface and the delta-negative or delta-positive dipoles on water molecules, when there is LEAST charge on the protein surface you can also expect their to be the least favourable interactions between water molecules and the protein. As the protein-water interaction is in competition with protein-protein interactions, being at the pI most favours protein-protein interactions, which leads to precipitation, compared to protein-water interaction which lead to solvation.
Isoelectric. "equal electric [charge]"
The previous answer is incorrect in multiple ways and correct in some. It states "protein solubility is based upon electrostatic interactions between the charges (negative or positive) on the protein surface and the ...dipoles of water". Firstly, there cannot exist an electrostatic interaction (coulombic) with one charged molecule and an uncharged water molecule/induced dipole. An electrostatic force of a charged particle must have an electrolyte in solution for interaction.
What the explanation aimed to describe is the decreased ion-induced dipole forces from a charged amino acid side chain to molecules of water at the pI of the protein. The singular force of which is stronger than H-bonding (and much stronger than van der waals, london/dispersion forces). Collectively H-bonding of the exterior amino acids is a much stronger force than total of the ion-induced dipoles.
...However, if we were talking about "solvation" of the molecule, then his answer would be completely correct where at the isoelectric point the least solvation would occur, largely due to the absence of charged outer residues...
Why is the solubility not dependent on ion-induced dipole? We only have 5 natural occurring amino acid R groups that can be charged around neutral pH: aspartate, glutamate - whose side chains behave as any other organic acid in the physiological range, reacting with other amine side chains, going through esterification with alcohols, chelation of divalent metal ions, etc.
The basic residues - lysine and arginine, lysine will undergo a number of reactions with or without a protonated nitrogen. Arginine however is likely going to carry a net charge at any protein pI and is the least reactive A.A. (however its' frequency in proteins is 5.7%, of this percent a fraction of which will go toward ion-dipole surface interaction with water. The same goes for histidine but it is even less frequent in proteins (2.2%).
The pI of most any protein will be nearer to the physiological range than to either extreme, so we can rule out mass protonation/deprotonation of side chains at its pI, which is the only way ion-induced dipole forces would participate in such solubility changes anyhow.
So what does make a protein soluble/insoluble in water?
A protein's 'solubility' comes first from the specific volume of water being much smaller than the specific volume of the protein. Meaning although our protein may be more dense than water, it has a tendency to be suspended in solution because of the much larger volume occupied (this of course is not true for many types of proteins, seen more in globular proteins but the theory is the same).
The major factor of protein solubility according to pI is hydrophilic residues (vs hydrophobic) on the exterior. As the pH of the solution nears an equilibrium of oxidation/reduction of the hydrophobic exterior residues, less water molecules are forming h-bonds, dipoles, van der waals, etc on the protein's exterior. You could imagine the H2O 'dispersing' away from the membrane, decreasing the volume occupied by H2O molecules near the protein exterior. This action allows the protein to 'fall' from solution and form a precipitate at the pI of the solution. The physical chemistry behind this action is much more involved, but this should give some idea of the biochemistry of the event.
A protein is least soluble at its isoelectric point because at this pH, the protein has no net charge and is less likely to interact with water molecules. This lack of charge reduces the protein's solubility, causing it to precipitate out of solution.
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The isoelectric point of an amino acid is?
The isoelectric point of an amino acid is the pH at which the amino acid carries no net charge. It is the pH at which the amino acid exists in its zwitterionic form, with equal numbers of positive and negative charges.
Why agarose gel electrophoresis is not used for protein analysis?
Agarose gel electrophoresis is primarily used for separating and analyzing nucleic acids based on their size, as it provides good resolution for DNA and RNA molecules. However, proteins have different properties (charge, size, and shape) compared to nucleic acids, making agarose gel less suitable for protein analysis. For protein analysis, techniques like SDS-PAGE and isoelectric focusing are commonly used, as they are designed specifically for separating proteins based on their size, charge, and isoelectric point.
The pI of a lysozyme is 11. What is the pH range in which the overall charge of the lysozyme is positive?
The overall charge of a protein is positive when the pH is below the pI (isoelectric point). For lysozyme with a pI of 11, the pH range in which its overall charge is positive would be below pH 11.
What is a mutation called that has no effect on an organism?
A point mutation, in which one nitrogen base in a codon is substituted for another, may have no effect on an organism. This is true if the base substitution does not change the amino acid that the codon represents, or if the mutation occurs in a non-critical location in the protein so that the protein's structure is not changed significantly and the protein is still able to function.
According to the graph below at which point is the plant performing the least photosynthesis?
For apex--- Point a.
What is the pI of a protein?
The pI (isoelectric point) of a protein is the pH at which the protein carries no net charge. It is the pH at which the protein will not migrate in an electric field.
What is isoelectric pH?
Isoelectric pH, often referred to as the pI (isoelectric point), is the pH at which a molecule or substance carries no net electrical charge. It is the pH at which the molecule is neutral or balanced between positive and negative charges. At the isoelectric pH, the molecule tends to be least soluble in water due to its minimum ionization state.
What is meant by isoelectric point of protein?
It is the pH at which a particular molecule or surface carries no net electrical charge
What is meant by isoelectronic point of protein?
The isoelectric point of a protein is the pH at which the protein has zero net charge. At this pH, the number of positively charged amino acids equals the number of negatively charged amino acids in the protein, resulting in a neutral overall charge.
How can you calculate the pH of NaHCO3 at its isoelectric point?
At the isoelectric point, the compound is neutral and does not exhibit acidic or basic properties. As NaHCO3 is a salt, its pH at the isoelectric point would be around 7, which is neutral. At this point, the concentration of H+ ions equals the concentration of OH- ions.
What is the isoelectric point of HBsAg?
4.5 to 5.5 . its acidic.
Protein electrophoresis and how its carried out?
Protein electrophoresis is a technique used to separate and analyze proteins in a mixture based on their size and charge. It involves applying an electric field to the protein sample placed in a gel matrix, causing the proteins to migrate based on their charge. The separated proteins can then be visualized using staining techniques to analyze their composition and relative abundance.
The isoelectric point of an amino acid is?
The isoelectric point of an amino acid is the pH at which the amino acid carries no net charge. It is the pH at which the amino acid exists in its zwitterionic form, with equal numbers of positive and negative charges.
What is point between qrs and st segment on ekg called?
what does isoelectric line represent
Is collagen basic or acidic?
Collagen is a protein and has an isoelectric point around pH 7, meaning it is electrically neutral at this pH. It contains both basic and acidic amino acids in its structure, which contribute to its overall neutral charge.
What happens to protein charge if pH value becomes lower than pi in 2 dimensional gel electrophoresis?
If the pH value becomes lower than the protein's isoelectric point (pI) in 2D gel electrophoresis, the protein will acquire a net positive charge due to the excess of protons. This will cause the protein to move towards the cathode during electrophoresis.
Why agarose gel electrophoresis is not used for protein analysis?
Agarose gel electrophoresis is primarily used for separating and analyzing nucleic acids based on their size, as it provides good resolution for DNA and RNA molecules. However, proteins have different properties (charge, size, and shape) compared to nucleic acids, making agarose gel less suitable for protein analysis. For protein analysis, techniques like SDS-PAGE and isoelectric focusing are commonly used, as they are designed specifically for separating proteins based on their size, charge, and isoelectric point.
