NADH peroxidase explained

NADH peroxidase
Ec Number:	1.11.1.1
Cas Number:	9032-24-0
Go Code:	0016692
Width:	296px

In enzymology, a NADH peroxidase is an enzyme that catalyzes the chemical reaction

NADH + H⁺ + H₂O₂

\rightleftharpoons NAD⁺ + 2 H₂O

The presumed function of NADH peroxidase is to inactivate H₂O₂ generated within the cell, for example by glycerol-3-phosphate oxidase during glycerol metabolism or dismutation of superoxide, before the H₂O₂ causes damage to essential cellular components.^[1]

The 3 substrates of this enzyme are NADH, H⁺, and H₂O₂, whereas its two products are NAD⁺ and H₂O. It employs one cofactor, FAD, however no discrete FADH₂ intermediate has been observed.^[2]

This enzyme belongs to the family of oxidoreductases, specifically those acting on a peroxide as acceptor (peroxidases). The systematic name of this enzyme class is NADH:hydrogen-peroxide oxidoreductase. Other names in common use include DPNH peroxidase, NAD peroxidase, diphosphopyridine nucleotide peroxidase, NADH-peroxidase, nicotinamide adenine dinucleotide peroxidase, and NADH2 peroxidase.

Structure

The crystal structure of NADH peroxidase resembles glutathione reductase with respect to chain fold and location as well as conformation of the prosthetic group FAD^[3]

His10 of the NADH peroxidase is located near the N-terminus of the R1 helix within the FAD-binding site.^[4] One of the oxygen atoms of Cys42-SO₃H is hydrogen-bonded both to the His10 imidazole and to Cys42 N terminus. The His10 functions in part to stabilize the unusual Cys42-SOH redox center. Arg303 also stabilizes the Cys42-SO₃H. Glu-14 participates in forming the tight dimer interface that limits solvent accessibility, important for maintaining the oxidation state of the sulfenic acid.

Reaction mechanism

The NADH peroxidase from Enterococcus faecalis is unique in that it utilizes the Cys42 thiol/sulfenic acid (-SH/-SOH) redox couple in the heterolytic cleavage of the peroxide bond to catalyze the two-electron reduction of hydrogen peroxide to water.^[5]

The kinetic mechanism of the wild-type peroxidase involves (1) NADH reduction of E(FAD, Cys42-SOH) to EH₂(FAD, Cys42-SH) in an initial priming step; (2) rapid binding of NADH to EH₂; (3) reduction of H₂O₂ by the Cys42-thiolate, yielding E•NADH; and (4) rate-limiting hydride transfer from bound NADH, regenerating EH₂.^[6] No discrete FADH₂ intermediate has been observed, however, and the precise details of Cys42-SOH reduction have not been elucidated.^[7]

1. E + NADH → (EH₂'•NAD⁺)* → EH₂'•NAD⁺ → EH₂ + NAD⁺ + H₂O
2. EH₂ + NADH → EH₂•NADH*
3. EH₂•NADH* + H₂O₂ → E•NADH + H₂O
4. E•NADH + H⁺ → EH₂•NAD⁺ + H₂O
5. EH₂•NAD⁺ → EH₂ + NAD⁺

Inhibitors include Ag⁺, Cl⁻, Co²⁺, Cu²⁺, Hg²⁺, NaN₃, Pb²⁺, and SO₄²⁻.^[8] At suboptimal H₂O₂ concentrations and concentrations of NADH that are saturating, NADH inhibits the peroxidase activity of the NADH peroxidase by converting the enzyme to an unstable intermediate. NAD⁺ behaves as an activator by reversing the equilibria that lead to the unstable intermediate, thus converting the enzyme to the kinetically active complex that reduces H₂O₂.^[9]

Biological Function

NADH eliminates potentially toxic hydrogen peroxide under aerobic growth conditions and represents an enzymatic defense available against H₂O₂-mediated oxidative stress. Second, the enzyme presents an additional mechanism for regeneration of the NAD⁺ essential to the strictly fermentative metabolism of this organism.^[10] The enzyme may also protect against exogenous H₂O₂ and contribute to bacterial virulence.^[11]

The actual function of NADH peroxidases and oxidases in plants is still unclear, but they could act in early signaling of oxidative stress through producing H₂O₂.^[12]

An alternative role may include regulation of H₂O₂ formation by NADH peroxidase and oxidase in cell wall loosening and reconstruction.^[13]

Notes and References

1. La Carbona S, Sauvageot N, Giard JC, Benachour A, Posteraro B, Auffray Y, Sanguinetti M, Hartke A . Comparative study of the physiological roles of three peroxidases (NADH peroxidase, Alkyl hydroperoxide reductase and Thiol peroxidase) in oxidative stress response, survival inside macrophages and virulence of Enterococcus faecalis . Mol. Microbiol. . 66 . 5 . 1148–63 . December 2007 . 17971082 . 10.1111/j.1365-2958.2007.05987.x . 40046805 . free .
2. Miller H, Poole LB, Claiborne A . Heterogeneity among the flavin-containing NADH peroxidases of group D streptococci. Analysis of the enzyme from Streptococcus faecalis ATCC 9790 . J. Biol. Chem. . 265 . 17 . 9857–63 . June 1990 . 10.1016/S0021-9258(19)38750-2 . free . 2161844 .
3. Stehle T, Claiborne A, Schulz GE . NADH binding site and catalysis of NADH peroxidase . Eur. J. Biochem. . 211 . 1–2 . 221–6 . January 1993 . 8425532 . 10.1111/j.1432-1033.1993.tb19889.x . free .
4. Book: Yeh JI, Claiborne A . Crystal Structures of Oxidized and Reduced Forms of NADH Peroxidase . Redox Cell Biology and Genetics Part B . 353 . 44–54 . 2002 . 12078517 . 10.1016/S0076-6879(02)53035-4 . Methods in Enzymology . 978-0-12-182256-9 . https://archive.org/details/redoxcellbiology353senc/page/44 .
5. Crane EJ, Yeh JI, Luba J, Claiborne A . Analysis of the kinetic and redox properties of the NADH peroxidase R303M mutant: correlation with the crystal structure . Biochemistry . 39 . 34 . 10353–64 . August 2000 . 10956025 . 10.1021/bi000553m.
6. Crane EJ, Parsonage D, Poole LB, Claiborne A . Analysis of the kinetic mechanism of enterococcal NADH peroxidase reveals catalytic roles for NADH complexes with both oxidized and two-electron-reduced enzyme forms . Biochemistry . 34 . 43 . 14114–24 . October 1995 . 7578008 . 10.1021/bi00043a016 .
7. Crane EJ, Parsonage D, Claiborne A . The active-site histidine-10 of enterococcal NADH peroxidase is not essential for catalytic activity . Biochemistry . 35 . 7 . 2380–7 . February 1996 . 8652580 . 10.1021/bi952347y .
8. Dolin MI . The Streptococcus faecalis oxidases for reduced diphosphopyridine nucleotide. III. Isolation and properties of a flavin peroxidase for reduced diphosphopyridine nucleotide . J. Biol. Chem. . 225 . 1 . 557–73 . March 1957 . 10.1016/S0021-9258(18)64952-X . free . 13416259 .
9. Dolin MI . DPNH peroxidase: effector activities of DPN . Biochem. Biophys. Res. Commun. . 78 . 1 . 393–400 . September 1977 . 199166 . 10.1016/0006-291X(77)91267-0. 2027.42/22844 . free .
10. Hansson L, Häggström MH . Effects of growth conditions on the activities of superoxide dismutase and NADH-oxidase/NADH-peroxidase inStreptococcus lactis . Current Microbiology . 1984 . 10 . 6 . 345–351 . 10.1007/BF01626563. 27660179 .
11. Gordon J, Holman RA, McLeod JW . Further observations on the production of hydrogen peroxide by anaerobic bacteria . J Pathol Bacteriol . 66 . 2 . 527–37 . October 1953 . 13118459 . 10.1002/path.1700660224 .
12. Šimonovičová M, Tamás L, Huttová J, Mistrík I . Effect of Aluminium on Oxidative Stress Related Enzymes Activities in Barley Roots . Biologia Plantarum . 2004 . 48 . 2 . 261–266 . 10.1023/B:BIOP.0000033454.95515.8a . 34802416 . free .
13. Chen SX, Schopfer P . Hydroxyl-radical production in physiological reactions. A novel function of peroxidase . Eur. J. Biochem. . 260 . 3 . 726–35 . March 1999 . 10103001 . 10.1046/j.1432-1327.1999.00199.x .