Medical Microbiology

162 3 GeneralBacteriology

Theroleofoxygen.Oxygenisactivatedinoneofthreeways:

&Transferof4e–toO 2 ,resultingintwooxygenions(2O2–).

&Transferof2e–toO 2 ,resultinginoneperoxideanion(1O 2 2–).

&Transferof1e–toO 2 ,resultinginonesuperoxideanion(1O 2 – ).

Hydrogenperoxideandthehighlyreactivesuperoxideanionaretoxicand

thereforemustundergofurtherconversionimmediately(seeFig.3. 15 ).

BacterialOxidationPathways

Fermentation

–Alcoholic fermentation

–Butyric acid fermentation

–etc.

Anaerobic respiration

• Nitrate respiration


• Sulfate respiration


• etc.

NAD catalysis

Flavin catalysis

Ubiquinone catalysis

Hemin catalysis

H 2 donor NNAADDH(P^2 )H

2

FADH 2

FMNH 2

Organic H 2

acceptor

H 2 O +^1 / 2 O 2

Catalase

GSSG + 2H 2 O

2 GSH e.g., glutathione peroxidase

H 2 O 2 H^2 O

2H 2 O

2H+

O 2 2–(= peroxide anion)

2H+

4H+ 2O2–

NO 3 –

SO 4 2–

NAD(P)H oxidase

FAD oxidase

O 2 – (= superoxide anion)

2O 2 – + 2H+

Superoxide dismutase

H 2 O 2 + O 2

2e–

4e–

2e–

1e–

Aerobic Respiration

Ubiquinone

Menaquinone

Porphyrins

(cytochromes,

siderotic

heme)

Fig.3. 15 Inoxidationoforganicnutrientsubstrates,protons(H+)andelectrons

(e–)aretransferredinmoreorlesslongchains.Therespirationisaerobicwhenthe

finalelectronacceptorisfreeoxygen.Anaerobicrespirationiswhentheelectrons

aretransferredtoinorganicallyboundoxygen.FermentationisthetransferofH+

ande–toanorganicacceptor.

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Kayser, Medical Microbiology © 2005 Thieme