U. C. Davis, Biological Sciences

Amino Acid Structure/Function

Sulfur-containing Amino Acids

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Aliphatic AA	Aromatic AA	Polar but Uncharged AA
G, A, V, L, I, P	F, Y, W	S, T, N, Q

Suflur Containing AA	Charged AA
C, M	D, E, H, K, R

Amino Acid

pK_a's²

Pro Structure³

Chemical Structure⁴

3-D Structure⁵

S

u

l

f

u

r

Cysteine, Cys, C
Sulfur analog of Ser
weak charge
forms disulfide bonds
not hydrophilic (0.17)
Molec. Wt. = 103
Mole % = 2.8

N=8.18

C=1.96

R=10.28

pI=5.07

a =0.66

ß =1.40

t =0.54

Methionine, Met, M
initiator of proteins
no charge
hydrophobic (1.1)
Molec. Wt. =131
Mole % = 1.7

N=9.21

C=2.28

pI=5.74

a =1.30

ß =1.14

t =0.52

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