Gene/Protein
Disease
Symptom
Drug
Enzyme
Compound
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Gene/Protein
Disease
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Target Concepts:
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Query: UMLS:C1832526 (
PCC
)
5,967
document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)
Protoporphyrinogen IX oxidase
(
PPO
), the last enzyme that is common to both chlorophyll and heme biosynthesis pathways, catalyzes the oxidation of protoporphyrinogen IX to protoporphyrin IX.
PPO
has several isoforms, including the oxygen-dependent HemY and an oxygen-independent enzyme, HemG. However, most cyanobacteria encode HemJ, the least characterized
PPO
form. We have characterized HemJ from the cyanobacterium
Synechocystis
sp.
PCC
6803 (
Synechocystis
6803) as a
bona fide
PPO
; HemJ down-regulation resulted in accumulation of tetrapyrrole precursors and in the depletion of chlorophyll precursors. The expression of FLAG-tagged
Synechocystis
6803 HemJ protein (HemJ.f) and affinity isolation of HemJ.f under native conditions revealed that it binds heme
b
The most stable HemJ.f form was a dimer, and higher oligomeric forms were also observed. Using both oxygen and artificial electron acceptors, we detected no enzymatic activity with the purified HemJ.f, consistent with the hypothesis that the enzymatic mechanism for HemJ is distinct from those of other
PPO
isoforms. The heme absorption spectra and distant HemJ homology to several membrane oxidases indicated that the heme in HemJ is redox-active and involved in electron transfer. HemJ was conditionally complemented by another
PPO
, HemG from
Escherichia coli.
If grown photoautotrophically, the complemented strain accumulated tripropionic tetrapyrrole harderoporphyrin, suggesting a defect in enzymatic conversion of coproporphyrinogen III to protoporphyrinogen IX, catalyzed by coproporphyrinogen III oxidase (CPO). This observation supports the hypothesis that HemJ is functionally coupled with CPO and that this coupling is disrupted after replacement of HemJ by HemG.
...
PMID:The cyanobacterial protoporphyrinogen oxidase HemJ is a new
b
-type heme protein functionally coupled with coproporphyrinogen III oxidase. 2992 90
