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Arginine is the amino acid with the formula (H 2 N)(HN)CN(H)(CH 2) 3 CH(NH 2)CO 2 H. The molecule features a guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO 2 −) and both the amino and guanidino groups are protonated, resulting in a cation.
See Amino acid for the pK a values of all amino acid side chains inferred in such a way. There are also numerous experimental studies that have yielded such values, for example by use of NMR spectroscopy. The table below lists the model pK a values that are often used in a protein pK a calculation, and contains a third column based on protein ...
Chemical formula: C 6 H 14 N 4 O 2 Molar mass: 174.2 g·mol −1 Systematic name: 2-amino-5-(diaminomethylidene amino)pentanoic acid Abbreviations: R, Arg Synonyms: 2-amino-5-guanidinopentanoic acid
The following table presents pK a values at 20 °C. Values change by about 0.01 per degree of temperature. [1] [3] Good's original 1966 paper had two older buffers (marked with italics) for comparison. In 1972 Good published a second list with three more buffers, and five more were added in 1980.
A knowledge of pK a values is important for the quantitative treatment of systems involving acid–base equilibria in solution. Many applications exist in biochemistry; for example, the pK a values of proteins and amino acid side chains are of major importance for the activity of enzymes and the stability of proteins. [67]
It appears that the pKa values in the arginine article might be in the wrong order. PubChem (Arginine, C6H14N4O2 - PubChem) lists arginine pKa values as pK1 = 2.18, pK2 = 9.09, and pK3 = 13.2. Mikestorm1 20:46, 14 April 2019 (UTC) Yes, only one pKa is listed, whereas the compound has 3 relevant values.
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N.D.: The pKa value of Pyrrolysine has not been reported. Note: The pKa value of an amino-acid residue in a small peptide is typically slightly different when it is inside a protein. Protein pKa calculations are sometimes used to calculate the change in the pKa value of an amino-acid residue in this situation.