Structure
•Contains a seven stranded beta sheet
•Seven alpha helices surround beta sheet
The large hydrophobic beta sheet is solubilzed by
the surrounding helices. COIII is thought to be a
dimer and holds the Coproporphyrin in the center
of two enzymes linked by interacting helicies.
sequence
11
41
81
121
161
201
241
281
321
341
Malqlgrlss
rsaagrvcrp
alaglvglat
f
gpcwlvargg cggprawsqc gggglrawsq
pgpagteqsr glghgstsrg gpwvgtglaa
aafghvqrae mlpktsgtra tslgrpeeee
mappvt
anf
g
dgcv
l
vlk tkdgkl
k nphap
ead gn
ptyl
g
rgi
dsp
dsf
rgt
p
gs
p
eym hsps
alignment
Function of Coproporphyrin Oxidase
Coproporphyrin Oxidase selectively doubly decarboxilates
Coproporphyrin Oxidase III, turning it into Protoporphyrin-IX.
Heme synthesis
Organic
Reaction
Transition state of
Coproporphyrin
The four pyrolles are
thought to coordinate
to an Aspartate and the
two propionate groups
to be decarboxylated
coordinate to arginine
groups.
Active site
The active site is thought to be Aspartate 400, Arginine 206, and 401.
Active site Km
Kinetic Studies of wild
COIII (above) compared
to mutagens of Asp 400,
Arg 262, and Arg 401
(Right)
Deficiency of Coproporphyrin Oxidase
Leafs with
various
mutagens in
COIII
As with all enzymes on the heme and chlorophyll synthetic pathways, a
deficiency of COIII causes a build up of precursors as well as a lack
porphyrin product. The build up leads to surface lesions , and sensitivity to
light in plants and animals.
references
• Lash, T.D. The enigma of coprpporphyrinogen oxidase: How
does this unusual enzyme carry out oxidative
decarboxylations to afford vinyl groups? Bio. & Med. Chem.
Lett. 2005, 4506-4509
• Stephenson, J.R.; Stacey J.A.; Morgenthaler, J. B; Friesen,
J.A.; Lash, T.D.; Jones, M.A. Role of aspartate 400, arginine
262, and arginine 401 in the catalytic mechanism of human
coproporphyrinogen oxidase Protein Science 2007, 41-410
• Ishikawa, A.; Okamato, H.; Iwasaki, Y.; Asahi, T.; A deficiency
of coproporphyrinogen III oxidase causes lesion formation
in Arabidopsis, The Plant Journal 2001, 89-99
• Nelson, D. L., & Cox, M. M. (2005). Lehninger Principles of
Biochemistry. New York: W.H. Freeman and Company.
Coproporphyrin Oxidase:
For America