Some strict anaerobic bacteria catalyze with glycine as substrate an internal Stickland reaction by which glycine serves as electron donor being oxidized by glycine-cleavage system or as electron acceptor being reduced by glycine reductase. In both cases, energy is conserved by substrate level phosphorylation. Except for the different substrate-activating proteins PB, reduction of sarcosine or betaine to acetyl phosphate involves in Eubacterium acidaminophilum the same set of proteins as observed for glycine, e.g. a unique thioredoxin system as electron donor and an acetyl phosphate-forming protein PC interacting with the intermediarily formed Secarboxymethylselenoether bound to protein PA.