TABLE 2.

Pairs of oxygen-tolerant and intolerant enzymes which catalyze the same reaction or are key enzymes of alternative pathways leading to the same products.

Pathway/Enzymes	Oxygen-tolerant	Oxygen-intolerant
Glutamate fermentation	Glutamate mutase B12	(R)-2-Hydroxyglutaryl-CoA dehydratase
Lactate, pyruvate, alanine, cysteine and serine fermentation to propionate	Methylmalonyl-CoA mutase B12	(R)-Lactyl-CoA dehydratase
Glycerol dehydratase	B12-dependent eliminase	Glycyl radical enzyme
Propane-1,2-diol dehydratase	B12-dependent eliminase	Glycyl radical enzyme
Ribonucleotide reductase	Class II: B12-dependent eliminase and reductase	Class III: Glycyl radical eliminase and reductase
Ethanolamine ammonia lyase	B12-dependent eliminase	−
Choline-trimethylamine lyase	−	Glycyl radical enzyme
Threonine and methionine fermentation to propionate and butyrate	TDP-dependent oxidation of 2-oxobutyrate to propionyl-CoA	Dehydration of (R)-2-hydroxybutyryl-CoA by (R)-lactyl-CoA dehydratase
Oxidation of 2-oxoacids to acyl-CoA	TDP-dependent enzymes: Pyruvate ferredoxin oxidoreductase; pyruvate dehydrogenase (NAD)	Glycyl radical enzyme: pyruvate:formate lyase (PFL)
Taurine fermentation	TDP-dependent enzyme: Sulfoacetaldehyde desulfonase	Glycyl radical enzyme: Isethionate lyase