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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
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 ...
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] Protein pK a values cannot always be measured directly, but may be calculated using theoretical methods.
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.
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.
The arginine group has a pKa of about 12.6 and is therefore unlikely to protonate the pyridine. Normally in PLP reactions an acidic amino acid residue such as a carboxylic acid group, with a pKa of about 5, protonates the pyridine ring. [8] The protonation of the pyridine nitrogen allows the nitrogen to accept additional negative charge.
In enzymology, an arginine-pyruvate transaminase (EC 2.6.1.84) is an enzyme that catalyzes the chemical reaction. L-arginine + pyruvate 5-guanidino-2-oxopentanoate + L-alanine. Thus, the two substrates of this enzyme are L-arginine and pyruvate, whereas its two products are 5-guanidino-2-oxopentanoate and L-alanine.