In the first step of glycine reductase, the substrate is bound to component PB via a Schiff base intermediate. Then the PB-activated substrate is nucleophilically attacked by the selenol anion of component PA to transform it to a carboxymethylated selenoether and the respective amine. By action of component PC, acetyl phosphate is formed, leaving component PA in its oxidized state. Finally component PA becomes reduced by the thioredoxin system to start a new catalytic cycle of reductive deamination. [thioredoxin]-disulfide + acetyl phosphate + H2O + NH4(+) = [thioredoxin]-dithiol + glycine + H(+) + phosphate Heterohexamer of two alpha, two beta and two gamma subunits. Component of the glycine reductase complex, together with components A and C. PB is substrate specific. The peptide chain is cleaved into beta and alpha chains, and the alpha chain N-terminal cysteine is deaminated and oxidized to form a reactive pyruvoyl group.