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prot pi – protein isoelectric point — an online program for calculating pI of proteins (include multiple subunits and posttranslational modifications) CurTiPot — a suite of spreadsheets for computing acid-base equilibria (charge versus pH plot of amphoteric molecules e.g., amino acids)
In computational biology, protein pK a calculations are used to estimate the pK a values of amino acids as they exist within proteins.These calculations complement the pK a values reported for amino acids in their free state, and are used frequently within the fields of molecular modeling, structural bioinformatics, and computational biology.
Also, amino acid side chain affinity for water was measured using vapor phases. [14] Vapor phases represent the simplest non polar phases, because it has no interaction with the solute. [18] The hydration potential and its correlation to the appearance of amino acids on the surface of proteins was studied by Wolfenden.
The isoionic point is the pH value at which a zwitterion molecule has an equal number of positive and negative charges and no adherent ionic species. It was first defined by S.P.L. Sørensen, Kaj Ulrik Linderstrøm-Lang and Ellen Lund in 1926 [1] and is mainly a term used in protein sciences.
Amino acids are composed of a side chain , a basic amino group, and a carboxyl group. Based on an aminos R group every amino acid will react different because of shape or composition. They can be divided into four different groups non polar amino acids, polar amino acids, positively charged, and negatively charged R group.
Five amino acids possess a charge at neutral pH. Often these side chains appear at the surfaces on proteins to enable their solubility in water, and side chains with opposite charges form important electrostatic contacts called salt bridges that maintain structures within a single protein or between interfacing proteins. [32]
The N-O distance required is less than 4 Å (400 pm). Amino acids greater than this distance apart do not qualify as forming a salt bridge. [11] Due to the numerous ionizable side chains of amino acids found throughout a protein, the pH at which a protein is placed is crucial to its stability.
This discrepancy can be traced back to the conformation in which the Gly-X-Gly tripeptides are evaluated to calculate MaxASA. The earlier works used the extended conformation, with backbone angles of ϕ = − 120 ∘ {\displaystyle \phi =-120^{\circ }} and ψ = 140 ∘ {\displaystyle \psi =140^{\circ }} .