Arginine is an essential amino acid in juvenile humans arginine is a complex amino acid often found at active site in proteins and enzymes due to its amine containing side chain. At physiological ph the carboxylic acid is deprotonated coo the amino group is protonated nh 3 and the guanidino group is also protonated to give the guanidinium form c nh 2 2 making arginine a charged aliphatic amino acid.
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Pk and pl values of amino acids.
Arginine pka. Pka 1 a carboxyl group pk a 2 a ammonium ion and pk a 3 side chain group. At ph 1 arinine is completely protonated. It is the precursor for the biosynthesis of nitric oxide.
9 key to all of these functions is the charge state and hence equilibrium acid dissociation. The pka of an amino acid depends upon its type group and side chains. For example when lysine is part of the carboxylic acid group it has a pka of 218 compared to a pka of 895 when it is part of the amino group and 1053 with side chains.
Amino acid pka values and side chain identities amino acid pka values a co 2h a nh 3 side side chain z fully protonated alanine 234 969 ch 3 arginine 217 904 1248 h 2ncnhch 2ch 2ch 2d nh2 asparagine 202 884 h2ncch2d o aspartic acid 209 982 386 ch 2co 2h cysteine 171 1078 833 ch 2sh. In these systems arginine acts in its fully protonated state as a modulator of the pk a values of the groups serving as proton donors and acceptors. Find the pka value that takes the amino acid from neutral to 1 234 for glycine and then find the halfway point or average.
The pk a values and the isoelectronic point pi are given below for the 20 a amino acids. As the ph increases and moves past each pka arinine gradually loses its acidic protons. Arginine may prevent or treat heart and circulatory diseases combat fatigue and stimulate the immune system.
The isoelectric point is the average of the 2 pka values that have a neutral molecule as one of its equilibrium species. 2 5 furthermore arginine has also been proposed to function as a general acidbase in a small number of enzymatic mechanisms 6 8 and its guanidinium moiety is a nucleophile or electrophile for a variety of post translational modifications. Inorganic 2 phenazine 24 phosphates 3 pyridine 25 carboxylic acids 4 8 pyrazine 26 aliphatic 4 8 aromatic 7 8 quinoline 27 phenols 9 quinazoline 27 alcohols and oxygen acids 10 11 quinoxaline 27 amino acids 12 special nitrogen compounds 28 peptides 13 hydroxylamines 28 nitrogen compounds 14 hydrazines 28 aliphatic amines 15 17 19.
Arginine is a polyprotic acid and therefore has three pka values.
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