Page 18 - Color Atlas of Biochemistry

Chemistry 9

A. cis–trans isomers B. Conformers

Fumaric acid Succinic acid
Fp. 287 °C Conformation 1
pK a 3.0, 4.5

Not rotatable Freely rotatable

Maleic acid Succinic
Fp. 130 °C acid
pK a 1.9, 6.5 Conformation 2

C. Optical isomers

Fischer projections

COO COO

C C
CH 3 CH 3
HO HO
COO OOC
H H
L(S) HO C H H C HO D(R)

CH 3 CH 3
L-lactic acid D-lactic acid
Fp. 53 °C 53 °C Fp.

pK a value 3.7 3.7 pK a value
Specific + 2.5˚ -2.5˚ Specific
rotation In muscle, blood In milk products rotation

D. The aconitase reaction

COO H 2 O OOC H H 2 O COO

H C H C H C OH
1 1 2
OOC C OH C OOC C H
OOC CH 2 COO 3
H C COO H C COO
2
2

Citrate (prochiral) cis-Aconitate (intermediate product) (2R,3S)-Isocitrate

trans-Aconitate occurs in plants 1 Aconitase 4.2.1.3

Koolman, Color Atlas of Biochemistry, 2nd edition © 2005 Thieme
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