Reversible thermally induced spin crossover in the myoglobin–nitrito adduct directly monitored by resonance Raman spectroscopy

Valianti, Vasiliki K.; Tselios, Charalampos; Pinakoulaki, Eftychia

doi:10.1039/d3ra00225j

Cited by 1 publication

(2 citation statements)

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“…The determined KD value of metAtHb3 is one order of magnitude lower than the wild-type myoglobin and very close to the H64Q mutant [53], indicating that the environment of the binding pocket, especially the distal histidine, plays an essential role in nitrite binding. A very interesting reversible thermally induced spin crossover in the myoglobin-nitrito adduct has also been recently observed, as revealed by Raman spectroscopy [54]. Even though ferric phytoglobins, or the so-called met form, presumably constitute a lower proportion of the entire Hb population in planta, due to the reducing environment, we consider them to be important from a mechanistic point of view.…”

Section: Structural Particularities and Ferric Phytoglobins Binding N...mentioning

confidence: 67%

Section: Resultsmentioning

confidence: 99%

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Redox Reactivity of Nonsymbiotic Phytoglobins towards Nitrite

Zagrean-Tuza,

Pato,

Damian

et al. 2024

Molecules

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Nonsymbiotic phytoglobins (nsHbs) are a diverse superfamily of hemoproteins grouped into three different classes (1, 2, and 3) based on their sequences. Class 1 Hb are expressed under hypoxia, osmotic stress, and/or nitric oxide exposure, while class 2 Hb are induced by cold stress and cytokinins. Both are mainly six-coordinated. The deoxygenated forms of the class 1 and 2 nsHbs from A. thaliana (AtHb1 and AtHb2) are able to reduce nitrite to nitric oxide via a mechanism analogous to other known globins. NsHbs provide a viable pH-dependent pathway for NO generation during severe hypoxia via nitrite reductase-like activity with higher rate constants compared to mammalian globins. These high kinetic parameters, along with the relatively high concentrations of nitrite present during hypoxia, suggest that plant hemoglobins could indeed serve as anaerobic nitrite reductases in vivo. The third class of nsHb, also known as truncated hemoglobins, have a compact 2/2 structure and are pentacoordinated, and their exact physiological role remains mostly unknown. To date, no reports are available on the nitrite reductase activity of the truncated AtHb3. In the present work, three representative nsHbs of the plant model Arabidopsis thaliana are presented, and their nitrite reductase-like activity and involvement in nitrosative stress is discussed. The reaction kinetics and mechanism of nitrite reduction by nsHbs (deoxy and oxy form) at different pHs were studied by means of UV-Vis spectrophotometry, along with EPR spectroscopy. The reduction of nitrite requires an electron supply, and it is favored in acidic conditions. This reaction is critically affected by molecular oxygen, since oxyAtHb will catalyze nitric oxide deoxygenation. The process displays unique autocatalytic kinetics with metAtHb and nitrate as end-products for AtHb1 and AtHb2 but not for the truncated one, in contrast with mammalian globins.

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Section: Structural Particularities and Ferric Phytoglobins Binding N...mentioning

confidence: 67%

Section: Resultsmentioning

confidence: 99%