| Functional annotation element | Key finding for *E. coli* K-12 Bcp (UniProt P0AE52) | Evidence |
|---|---|---|
| Enzymatic reaction / primary function | Thioredoxin-dependent peroxiredoxin (BCP/PrxQ subfamily) that reduces hydrogen peroxide and organic hydroperoxides, including *t*-butyl hydroperoxide, cumene hydroperoxide, and linoleic acid hydroperoxide; described as an unusually versatile bacterial peroxiredoxin. | (pqac-00000000, pqac-00000001, pqac-00000003, pqac-00000004, pqac-00000007) |
| Substrate preference | Early assays found strongest preference for linoleic acid hydroperoxide among tested substrates; later kinetic work showed broad peroxide specificity, with comparable rates for H2O2 and cumene hydroperoxide under some assay conditions. | (pqac-00000000, pqac-00000001, pqac-00000004) |
| Reducing partners | Physiological electron donor system is thioredoxin/thioredoxin reductase/NADPH; Trx1 directly supports activity in stopped-flow and NADPH-coupled assays. Bcp can also use Trx2 and glutaredoxins Grx1 and Grx3 as alternative reducing partners, indicating relaxed reductant specificity. | (pqac-00000000, pqac-00000001, pqac-00000003, pqac-00000005, pqac-00000007) |
| Catalytic residues / motif | Active-site motif is CPXXXXCR. Cys45 is the peroxidatic cysteine (Cp) and Cys50 is the resolving cysteine (Cr); Cys99 is present but not the primary catalytic thiol. C45S abolishes detectable Trx-dependent peroxidase/antioxidant activity. | (pqac-00000000, pqac-00000004, pqac-00000007, pqac-00000008) |
| Catalytic mechanism | Atypical 2-Cys peroxiredoxin: Cp (Cys45) is oxidized by peroxide to sulfenic acid, then resolved by Cr (Cys50) to form disulfide intermediates; both intra- and intersubunit disulfide-bonded forms were observed. Steady-state analysis is consistent with a ping-pong mechanism and a nonsaturable interaction with Trx1. | (pqac-00000000, pqac-00000001, pqac-00000006, pqac-00000007) |
| Kinetics: early substrate panel | Reported Km values: H2O2 47.8 µM, *t*-BHP 37.4 µM, linoleic acid hydroperoxide 11.7 µM. Vmax values: 7.01, 1.93, and 8.23 min^-1, respectively (also reported as 400, 110, and 469 nmol min^-1 mg^-1). Vmax/Km values: 0.147, 0.052, and 0.703 mmol min^-1 mmol^-1, respectively. | (pqac-00000000, pqac-00000004) |
| Kinetics: revised steady-state analysis | Bisubstrate stopped-flow analysis with Trx1 gave apparent Km for H2O2 of ~80 µM at 10 µM Trx1 and catalytic efficiency (Vmax/Km)app for H2O2 of ~1.3 × 10^4 M^-1 s^-1; extrapolated global-fit values for Trx gave Km ≈ 500 µM and Vmax ≈ 64 s^-1, though poorly constrained. | (pqac-00000001, pqac-00000006, pqac-00000010) |
| Assay conditions underlying kinetics | Key direct peroxidase assays used Trx, thioredoxin reductase, and NADPH at pH 7.0; stopped-flow rates were measured over the first 2 s at 25 °C, and peroxide consumption was also monitored by FOX assay in steady-state analyses. | (pqac-00000002, pqac-00000003, pqac-00000006) |
| Oligomeric state | Bcp is monomeric in solution up to at least 200 µM; sedimentation coefficients were ~2 S, and shape-independent molecular masses were 19.4 kDa (reduced) and 22.2 kDa (oxidized), with no higher-order oligomers observed under tested conditions. Earlier work also described the protein as monomeric (~18 kDa) irrespective of redox state. | (pqac-00000004, pqac-00000006) |
| Redox properties | Peroxidatic Cys45 has a measured pKa of ~5.8. Bcp has a relatively high redox midpoint potential of −145.9 ± 3.2 mV, supporting the idea that it can remain reduced under relatively oxidizing intracellular conditions. | (pqac-00000001, pqac-00000007) |
| Regulation / expression | A *bcp* promoter-*lacZ* fusion showed ~3-fold higher β-galactosidase activity during aerobic versus anaerobic growth, indicating oxygen-responsive expression. Evidence in the retrieved sources does not directly establish *bcp* as an OxyR regulon member, although a candidate reductant (Trx2) is strongly OxyR-induced during oxidative stress. | (pqac-00000008, pqac-00000009) |
| Physiological role / phenotype | Bcp contributes to oxidative-stress defense and redox homeostasis as a cytosolic peroxide-detoxifying enzyme in the thioredoxin/glutaredoxin network. The retrieved E. coli-focused sources provide strong biochemical evidence but limited direct in vivo mutant phenotype data for E. coli itself. | (pqac-00000000, pqac-00000001, pqac-00000007, pqac-00000008) |
| Cellular localization | No direct experimental localization for *E. coli* Bcp was reported in the retrieved sources. Given the lack of signal peptide/transmembrane annotations in the core biochemical literature and its use of cytosolic Trx/Grx systems, the best-supported annotation is cytosolic localization, but this remains inference rather than direct localization evidence in the cited papers. | (pqac-00000001, pqac-00000003, pqac-00000005) |


*Table: This table summarizes the most important functional annotation points for *Escherichia coli* K-12 Bcp/PrxQ (P0AE52), including enzymatic activity, substrates, catalytic residues, kinetics, redox properties, regulation, and phenotype evidence. It is useful as a compact evidence-backed reference for gene function curation.*