ionisable amino acids and pH at which it occurs

name all ionisable amino acids

• aspartic acid

• glutamic acid

• histidine

• cysteine

• lysine

• tyrosine

• arginine

which amino acid has the highest pka

arginine

which amino acids have the lowest pka

• glutamic acid

• aspartic acid

positively charged amino acids at physiological pH

• lysine

• arginine

• histidine

neg charged at physiological pH

• aspartic acid

• glutamic acid

neutral at physiological pH but can ionise

• cysteine

• tyrosine

lysine side chain pKa and pH it is protonated

• 10.5 pKa

• pH 7.4

arginine side chain pKa and pH it is protonated

• pKa 12.5

• pH 7.4

histidine side chain pKa and pH it is protonated

• pKa 6.0

• partially protonated at pH 7.4

aspartic acid side chain pKa and pH it is deprotonated

• pKa 3.9

• pH 7.4

glutamic acid side chain pKa and pH it is deprotonated

• pKa 4.2

• pH 7.4

cysteine side chain pKa and pH it becomes negatively charged

• pKa 8.3

• neutral at pH 7.4

• neg charged at higher

tyrosine side chain pKa

• pKa 10.4

• neutral at pH 7.4

• becomes neg charged at higher

what forms are favoured when pH > pKa, and pH< pKa

• when pH > pKa → deprotonated form, basic

• when pH< pKa → protonated form, acidic