What Is the Isoelectric Point?

The isoelectric point is the pH at which a molecule or surface is uncharged. For charged substances, it is not limited to ampholytes such as amino acids and proteins. Of course, protein is an amphoteric electrolyte, and its isoelectric point is related to the amount of acidic and basic amino acids it contains. The isoelectric point of various proteins is different due to the composition of amino acid residues. When the solution has a certain pH value, the positive and negative charges of the protein are exactly equal (the total net charge is zero), and it does not move to the anode or the cathode in the electric field. Therefore, the isoelectric point of a protein can be determined by electrophoresis, and protein molecules with different charging properties and different sizes and shapes can be separated and purified. At the isoelectric point, proteins do not have the same charge and repel each other, so they are the most unstable and have the lowest solubility. They are easily combined by electrostatic attraction to form larger aggregates, so they precipitate. At the same time, the viscosity, osmotic pressure, swellability and conductivity of the protein are all the smallest. (Zhang Lin) ^[1]

Isoelectric point

The isoelectric point is the pH at which a molecule or surface is uncharged. For charged substances, it is not limited to ampholytes such as amino acids and proteins. Of course, protein is an amphoteric electrolyte, and its isoelectric point is related to the amount of acidic and basic amino acids it contains. The isoelectric point of various proteins is different due to the composition of amino acid residues. When the solution has a certain pH value, the positive and negative charges of the protein are exactly equal (the total net charge is zero), and it does not move to the anode or the cathode in the electric field. Therefore, the isoelectric point of a protein can be determined by electrophoresis, and protein molecules with different charging properties and different sizes and shapes can be separated and purified. At the isoelectric point, proteins do not have the same charge and repel each other, so they are the most unstable and have the lowest solubility. They are easily combined by electrostatic attraction to form larger aggregates, so they precipitate. At the same time, the viscosity, osmotic pressure, swellability and conductivity of the protein are all the smallest. (Zhang Lin) ^[1]

Isoelectric point (pI, isoelectric point)

Amino acids have amino and

Isoelectric point: an amino acid is at a net charge of zero

Protein isoelectric point (reference value) ^[3]

Protein isoelectric point

Salmon Proline [salmine] 12.1

Herring protein [clupeine] 12.1

Protamine [sturline] 11.71

[Thymohistone] 10.8

Globin (human) [globin (human)] 7.5

Ovalbumin [ovalbuin] 4.71; 4.59

Conal bumin 6.8; 7.1

Serum albumin 4.7-4.9

Myoalbumin 3.5

Myosin [myogen A] 6.3

-lactoglobulin 5.1-5.3

Yolk protein [livetin] 4.8-5.0

1-globulin (human) [1-globulin (human)] 5.8; 6.6

2-globulin (human) [2-globulin (human)] 7.3; 8.2

Myosin A 5.2-5.5

Myosin A 5.1

Transferrin [siderophilin] 5.9

Fetuin 3.4-3.5

Fibrinogen 5.5-5.8

Alpha-Crystallin [-crystallin] 4.8

-ocular crystal protein [-crystallin] 6

Peanut Globulin [arachin] 5.1

With peanut protein [conarrachin] 3.9

Keratins 3.7-5.0

Reduced keratin [keratein] 4.6-4.7

Collagen [collagen] 6.5-6.8

Fish gel [ichthyocol] 4.8-5.2

White gelatin [gelatin] 4.0-4.1

-casein [-casein] 4.0-4.1

-casein [-casein] 4.5

-casein [-casein] 5.8-6.0

Alpha-ovalcoherin [-ovomucoid] 3.83-4.41

1-mucoprotein [1-mucoprotein] 1.8-2.7

Yolk Mucin [vitellomucoid] 5.5

Urinary gonadotropin 3.2-3.3

Lysozyme [lyso zyme] 11.0-11.2

Myoglobin 6.99

Hemoglobin (human) 7.07

Hemoglobin (chicken) [hemoglobin (hen)] 7.23

Hemoglobin (horse) [hemoglobin (horse)] 6.92

Hemocyanin [hemerythrin] 4.6-6.4

Earthworm hemoglobin [chlorocruorin] 5.6

Chlorocruorin 4.3-4.5

Invertebrate hemoglobin [erythrocruorins] 4.6-6.2 Cytochrome C 9.8-10.1

Rhodopsin [rhodopsin] 4.47-4.57

Thromboplastin [thromboplastin] 5.2

1-lipoprotein [1-lipoprotein] 5.5

1-lipoprotein [1-lipoprotein] 5.4

-lipovitellin [5.9]

Turnip yellow vvirus 3.75

Vaccinia virus [vaccinia virus] 5.3

Growth hormone [somatotropin] 6.85

Prolactin 5.73

Insulin [insulin] 5.35

Pepsin [pepsin] around 1.0

Chymotrypsin (chymotrypsin) 8.1

Bovine serum albumin 4.9

Ribonuclease or Rnase (bovine pancreas)] 7.8

Thyroglobulin 4.58

Thymonucleohistone around 4