In vivo distribution of phosphothioredoxin and thioredoxin in Escherichia coli

The phosphorylation state of thioredoxin was compared in intact cells and in crude extracts. In crude extracts, the extent of phosphorylation was 0.70 to 0.80 mol of phosphate per mol of thioredoxin, with approximately equal amounts of thioredoxin phosphorylated either on cysteinyl32 (formula: see text) or on cysteinyl35 (formula: see text). By comparison, the extent of thioredoxin phosphorylation in intact cells was nearly 1.0 with phosphate present almost exclusively on cysteine32. Nonphosphorylated thioredoxin was present as the reduced thiol form (formula: see text). These findings imply that (formula: see text) is the relevant in vivo species and that a mechanism is operative in crude extracts for transfer of phosphate from cysteine32 to cysteine35.