Download amino acid data - ChemConnections

Fundamentals
While their name implies that amino acids are
compounds that contain an —NH2 group and a
—CO2H group, these groups are actually
present as —NH3 + and —CO2– respectively.
Amino Acids
They are classified as α, β, γ , etc.
etc. amino acids
according the carbon that bears the nitrogen.
Amino Acids
+
NH3
α
CO2–
+
–
H3 NCH2 CH2CO2
β
+
–
H3 NCH2 CH2CH2CO2
γ
The 20 (22) Key Amino Acids
an α-amino acid that is an
intermediate in the biosynthesis
of ethylene
More than 700 amino acids occur naturally, but
20 (22?)of them are especially important.
a β -amino acid that is one of
the structural units present in
coenzyme A
They differ in respect to the group attached to
the α carbon.
a γ -amino acid involved in
the transmission of nerve
impulses
These 22 amino acids are the building blocks of
proteins. All are α-amino acids.
See Handout.
Amino Acids
+
H3 N
H
C
Amino Acids
O
C
O
–
R
The amino acids obtained by hydrolysis of
proteins differ in respect to R (the side chain).
The properties of the amino acid vary as the
structure of R varies.
Glycine
(Gly or G)
+
H3 N
H
O
C
C
O
–
H
Glycine is the simplest amino acid. It is the only
one in the table that is achiral.
achiral.
In all of the other amino acids in the table the α
carbon is a stereogenic center.
Amino Acids
+
H3 N
H
C
Amino Acids
O
C
O
–
+
H3 N
CH3
H
O
C
C
Valine
(Val or V)
Amino Acids
Amino Acids
H
C
O
C
O
–
+
H3 N
CH2CH(CH3 )2
H
O
C
C
Isoleucine
(Ile or I)
Amino Acids
Amino Acids
H
C
O
C
CH3SCH2 CH2
Methionine
(Met or M)
O
–
O
–
CH3CHCH2CH3
Leucine
(Leu or L)
+
H3 N
–
CH(CH3)2
Alanine
(Ala or A)
+
H3 N
O
+
H2 N
H2 C
H
O
C
C
C
H2
CH2
Proline
(Pro or P)
O
–
Amino Acids
+
H3 N
H
O
C
C
Amino Acids
O
–
+
H3 N
CH2
H
O
C
C
O
–
CH2
Tryptophan
N
Phenylalanine
(Phe or F)
H
Amino Acids
+
H3 N
H
C
Amino Acids
O
C
(Trp or W)
O
–
H2 NCCH2
+
H3 N
H
O
C
C
O
Asparagine
(Asn or N)
Glutamine
(Gln or Q)
Amino Acids
Amino Acids
H
C
–
H2 NCCH2CH2
O
+
H3 N
O
O
C
CH2OH
Serine
(Ser or S)
O
–
+
H3 N
H
O
C
C
CH3CHOH
Threonine
(Thr or T)
O
–
Amino Acids
+
H3 N
–
H
C
Amino Acids
O
C
O
+
H3 N
–
H
O
C
C
O
–
OCCH2 CH2
OCCH2
O
O
Aspartic Acid
(Asp or D)
Glutamic Acid
(Glu or E)
Amino Acids
Amino Acids
+
H3 N
H
C
–
O
C
O
+
H3 N
–
CH2
H
O
C
C
O
–
CH2SH
Cysteine
(Cys or C)
Tyrosine
(Tyr or Y)
OH
Amino Acids
+
H3 N
H
C
Amino Acids
O
C
O
–
+
CH2CH2 CH2CH2NH3
Lysine
(Lys or K)
+
H3 N
H
O
C
C
O
–
CH2CH2 CH2NHCNH 2
+ NH2
Arginine
(Arg or R)
Amino Acids: #21
(2001)
Amino Acids
+
H3 N
H
O
C
C
O
–
CH2
Selenocysteine
N
NH
Histidine
(His or H)
Amino Acids: #22
(2002)
Amino Acids: #22
(2002)
CO2 H
H2 N
X=
CH3
HN
N
NH2
CO
X
OH
Pyrrolysine (4 R, 5 R)
Pyrrolysine
Amino Acids with Neutral Side Chains
Acid-Base Behavior of Amino Acids
Glycine
+
H3 N
H
O
C
C
H
O
–
pKa1 = 2.34
pKa2 = 9.60
pI = 5.97
Amino Acids with Neutral Side Chains
Alanine
+
H3 N
H
C
O
C
O
–
Amino Acids with Neutral Side Chains
pKa1 = 2.34
pKa2 = 9.69
pI = 6.00
Valine
+
H3 N
CH3
Leucine
H
C
O
C
O
–
pKa1 =
pKa2 =
pI =
2.36
9.60
5.98
Methionine
C
CH3SCH2 CH2
C
O
–
pKa1 = 2.32
pKa2 = 9.62
pI = 5.96
Isoleucine
+
H3 N
O
C
O
–
H
O
C
C
O
–
pKa1 =
pKa2 =
pI =
2.36
9.60
5.98
CH3CHCH2CH3
Amino Acids with Neutral Side Chains
H
C
Amino Acids with Neutral Side Chains
CH2CH(CH3 )2
+
H3 N
O
CH(CH3)2
Amino Acids with Neutral Side Chains
+
H3 N
H
pKa1 = 2.28
pKa2 = 9.21
pI = 5.74
Amino Acids with Neutral Side Chains
Proline
+
H2 N
H2 C
H
O
C
C
C
H2
CH2
O
–
pKa1 = 1.99
pKa2 = 10.60
pI = 6.30
Side Chains
Phenylalanine
+
H3 N
H
C
Amino Acids with Neutral Side Chains
O
C
O
–
CH2
pKa1 = 1.83
pKa2 = 9.13
pI = 5.48
Tryptophan
+
H3 N
H
O
C
C
O
–
CH2
pKa1 = 2.83
pKa2 = 9.39
pI = 5.89
N
H
Amino Acids with Neutral Side Chains
Asparagine
+
H3 N
H
C
O
C
O
–
H2 NCCH2
pKa1 =
pKa2 =
pI =
Amino Acids with Neutral Side Chains
2.02
8.80
5.41
Glutamine
Serine
C
O
C
C
O
–
pKa1 =
pKa2 =
pI =
2.17
9.13
5.65
O
Amino Acids with Neutral Side Chains
H
H
H2 NCCH2CH2
O
+
H3 N
+
H3 N
O
C
CH2OH
O
–
pKa1 = 2.21
pKa2 = 9.15
pI = 5.68
Amino Acids with Neutral Side Chains
Threonine
+
H3 N
H
O
C
C
CH3CHOH
O
–
pKa1 = 2.09
pKa2 = 9.10
pI = 5.60
Amino Acids with Ionizable Side Chains
+
H3 N
Aspartic acid
–
H
C
O
C
O
–
OCCH2
pKa1 =
pKa2 =
pKa3 =
pI =
Amino Acids with Ionizable Side Chains
1.88
3.65
9.60
2.77
+
H3 N
Glutamic acid
–
H
O
C
C
O
–
OCCH2 CH2
O
pKa1 =
pKa2 =
pKa3 =
pI =
2.19
4.25
9.67
3.22
O
For amino acids with acidic side chains, pI is the
average of pK
pKa1 and pK
pKa2.
Amino Acids with Ionizable Side Chains
+
H3 N
Tyrosine
H
O
C
C
O
CH2
–
pKa1 =
pKa2 =
pKa3 =
pI =
Amino Acids with Ionizable Side Chains
2.20
9.11
10.07
5.66
Cysteine
+
H3 N
H
O
C
C
O
–
CH2SH
pKa1 =
pKa2 =
pKa3 =
pI =
1.96
8.18
10.28
5.07
OH
Amino Acids with Ionizable Side Chains
+
H3 N
H
O
C
C
O
–
+
CH2CH2 CH2CH2NH3
pKa1 =
pKa2 =
pKa3 =
pI =
Amino Acids with Ionizable Side Chains
2.18
8.95
10.53
9.74
+
H3 N
H
O
C
C
O
CH2CH2 CH2NHCNH 2
+ NH2
Lysine
For amino acids with basic side chains, pI is the
average of pK
pKa2 and pK
pKa3.
–
Arginine
pKa1 =
pKa2 =
pKa3 =
pI =
2.17
9.04
12.48
10.76
Amino Acids with Ionizable Side Chains
Histidine
+
H3 N
H
C
CH2
N
NH
O
C
O
–
pKa1 =
pKa2 =
pKa3 =
pI =
1.82
6.00
9.17
7.59