| Functional aspect | Key statements | Evidence type | Quantitative data | Key references with year and DOI URL | PaperQA citation IDs |
|---|---|---|---|---|---|
| O2 transport/buffering | PvLba is a highly abundant nodule hemeprotein whose essential role is O2 transport/delivery to symbiosomes while buffering free O2 to protect nitrogenase. Closely related leghemoglobins in legumes occur at millimolar concentrations and help maintain very low free O2 in infected cells. | Primary; review | Lb abundance in nodules ~1–5 mM; free O2 reported as <50 nM in nodules in recent legume literature. | Sainz et al., 2015, *Plant J.* DOI: https://doi.org/10.1111/tpj.12762; Minguillón et al., 2024, *J Exp Bot* DOI: https://doi.org/10.1093/jxb/erad455 | (pqac-00000001, pqac-00000008, pqac-00000009) |
| NO/ROS chemistry | PvLba reacts with reactive nitrogen/oxygen species; ferrous Lb binds NO to form LbNO, and Lbs can convert NO-derived species to nitrate in vitro. Recent mutant data in Lotus indicate that loss of Lbs causes NO and ROS accumulation, supporting a conserved role in nodule redox homeostasis. | Primary; review | In vitro PvLba nitration assays used ~10 µM ferric Lb, 20–100 µM H2O2, and ~100 µM nitrite; nitrate treatments in Lotus study were 0, 0.5, 5, 10 mM KNO3 for 2 d. | Sainz et al., 2015, https://doi.org/10.1111/tpj.12762; Minguillón et al., 2024, https://doi.org/10.1093/jxb/erad455 | (pqac-00000000, pqac-00000001, pqac-00000008, pqac-00000010, pqac-00000011) |
| Post-translational modifications | PvLba is nitrated in functional bean nodules, predominantly at Tyr30 in the distal heme pocket, indicating in vivo modification by nitrite/peroxide chemistry. This supports that LBA is an active redox-reactive globin in nodules rather than a passive O2 carrier only. | Primary | Young bean nodules contained ~0.23% nitrated PvLba; in vitro nitration reached ~25–70% under tested oxidant/nitrite conditions; nitration decreased in senescent and nitrate-treated nodules. | Sainz et al., 2015, https://doi.org/10.1111/tpj.12762 | (pqac-00000000, pqac-00000007) |
| Regulation by nitrate/stress | Recent legume data show Lb genes are strongly down-regulated by nitrate and dark stress, with nitrate-responsive promoter elements implicated. This is relevant to PvLba annotation because leghemoglobin expression is tightly coupled to nodule physiological state and N-fixation activity. | Primary | Nitrate suppressed Lbs after 2 d exposure to 0.5–10 mM KNO3; compensatory regulation between Lb paralogs was observed in Lotus mutants. | Minguillón et al., 2024, https://doi.org/10.1093/jxb/erad455 | (pqac-00000008, pqac-00000010, pqac-00000011, pqac-00000012) |
| Role in senescence/defense | Leghemoglobin is a marker of functional pink nodules; oxidation/decrease of Lb accompanies senescence and loss of N-fixation capacity. Reviews and recent studies connect Lb decline with nitro-oxidative stress, defense activation, and senescence-associated changes in antioxidants and proteolysis. | Review; primary | Nodule N2-fixation peak ~4 weeks and lifespan ~10–12 weeks in a recent synthesis; antioxidants in nodules include ascorbate ~1–2 mM and glutathione ~0.5–1 mM; APX ~0.9% of soluble protein. | Berrabah et al., 2024, *Plant Commun.* DOI: https://doi.org/10.1016/j.xplc.2024.100888; Minguillón et al., 2024, https://doi.org/10.1093/jxb/erad455 | (pqac-00000014, pqac-00000009, pqac-00000010, pqac-00000013) |
| Applications in food/fermentation | Although not specific to PvLba from bean, closely related leghemoglobins are used as heme/flavor-color ingredients in plant-based meat and are being optimized by precision fermentation in yeasts. Recent biotech studies report substantially improved recombinant production titers. | Biotech; review | K. marxianus intracellular LBA reached 7.27 g/L in 5 L fermentor with heme content 66.32 mg/L; S. cerevisiae intracellular LegH reached 544.8 mg/L and secreted LegH 88.5 mg/L; another K. phaffii process reported highest biomass density 121.80 gDCW/L and LegH yield 0.513 mg/gDCW. | Tian et al., 2024, *Front Bioeng Biotechnol.* DOI: https://doi.org/10.3389/fbioe.2023.1329016; Huang et al., 2024, *Fermentation* DOI: https://doi.org/10.3390/fermentation10030146; Suleiko et al., 2024, *Fermentation* DOI: https://doi.org/10.3390/fermentation10010055 | (pqac-00000022, pqac-00000016) |
| Safety/exposure data | Regulatory assessments of soy leghemoglobin produced in GM yeast concluded no safety concern at proposed use levels in meat analogues, though these data apply to soy LegH rather than bean PvLba directly. The evidence is still useful for real-world implementation of the leghemoglobin protein class. | Regulatory | Proposed maximum use level 0.8% soy leghemoglobin protein in meat analogues; mean dietary exposure up to 7.3 mg/kg bw/day and 95th percentile up to 32.9 mg/kg bw/day; NOAEL in 90-day study at highest tested doses corresponded to 2328 mg/kg bw/day (males) and 2865 mg/kg bw/day (females) soy leghemoglobin. | Younes et al., 2024, *EFSA J.* DOI: https://doi.org/10.2903/j.efsa.2024.8822; Casacuberta et al., 2024, *EFSA J.* DOI: https://doi.org/10.2903/j.efsa.2024.9060 | (pqac-00000015, pqac-00000017, pqac-00000018, pqac-00000019, pqac-00000021) |


*Table: This table summarizes the functional annotation of Phaseolus vulgaris leghemoglobin A (PvLba; UniProt P02234) using direct bean evidence where available and closely related leghemoglobin evidence for conserved functions, regulation, applications, and safety context.*