22
chapter
2
Amino Acids
COOH
1
HN—
2*
— C— H
Is
3
1
H2C \ 4^ C H 2
H
OH
4-Hydroxyproline
COOH
I
H2N—
c
— H
CH2
!
CH2
HC— OH
Present in collagen, a fibrous protein.
CH2
NH2
COOH
H,N— C— H
]
CH,
I
o
Phosphorylation and dephosphorylation
of selected serine residues in a variety
of proteins play an important role in
the regulation of metabolism and are
mediated by some hormones.
HO— P— OH
O
O-Phosphoserine
COOH
I
H,N— C— H
CH2
CH2
CH2
eCH,
N
H
CH3
e-N-Methyllysine
The N-trimethyl derivative
of lysine is involved in
the synthesis of carnitine.
COO-
HN
---------C— H
O—
^/CH
2
c
H2
5-Hydroxy
lysine
COOH
H2N— C— H
CH,
I
c = c
H
3
C - N ^
J|
c
H
3-Methylhistidine
Present in myosin, a muscle protein.
COOH
I
H,N— C— H
I
CH,
H N ^ ^ n
ch,
CH,
H
H,N
O
Diphthamide
A novel derivative of histidine present only in the eukaryotic protein
elongation factor 2 (EF-2), which participates in the elongation step of
protein biosynthesis. Diphtheria toxin inhibits eukaryotic protein synthesis
COOH
by catalyzing a covalent modification of diphthamide (see Chapter 25).
H,N— C— H
I
CH2
HOOC
CH
COOH
Pyrroiidone carboxylate
(pyroglutamate)
Present in some proteins and peptides
as N-terminai amino acid residue.
7-Carboxyglutamic acid
Present in certain blood-clotting proteins
H,N
COOH
CH
H,hk
HOOC'"
; c h — (c h j
(ÇHJ
(c h t — c h ;
,NH,
COOH
(ÇHJ,
H2N
COOH
Desmosine
Desmosine and isodesmosine are formed from iysyl residues
of the polypeptide chains of elastin, a fibrous protein.
FIGURE 2-6
Modified derivatives of certain amino acids are found in proteins.
