1JA8

Kinetic Analysis of Product Inhibition in Human Manganese Superoxide Dismutase

Summary for 1JA8

• Entry DOI: 10.2210/pdb1ja8/pdb
• Related: 1ABM 1AP5 1AP6 1EM1
• Descriptor: Manganese Superoxide Dismutase, MANGANESE (II) ION, SULFATE ION, ... (4 entities in total)
• Functional Keywords: manganese, superoxide, disumtase, sod, mnsod, homo sapien, alpha-beta, two-domain, homotetramer, hydrogen bond network, oxidoreductase
• Biological source: Homo sapiens (human)
• Cellular location: Mitochondrion matrix: P04179
• Total number of polymer chains: 2
• Total formula weight: 44730.09

Authors

Hearn, A.S.,Stroupe, M.E.,Cabelli, D.E.,Lepock, J.R.,Tainer, J.A.,Nick, H.S.,Silverman, D.S. (deposition date: 2001-05-29, release date: 2001-06-06, Last modification date: 2023-08-16)

Primary citation

Hearn, A.S.,Stroupe, M.E.,Cabelli, D.E.,Lepock, J.R.,Tainer, J.A.,Nick, H.S.,Silverman, D.N.
Kinetic analysis of product inhibition in human manganese superoxide dismutase.
Biochemistry, 40:12051-12058, 2001

PubMed Abstract: Manganese superoxide dismutase (MnSOD) cycles between the Mn(II) and Mn(III) states during the catalyzed disproportionation of O(2)(*-), a catalysis that is limited at micromolar levels of superoxide by a peroxide-inhibited complex with the metal. We have investigated the role in catalysis and inhibition of the conserved residue Trp161 which forms a hydrophobic side of the active site cavity of MnSOD. Crystal structures of mutants of human MnSOD in which Trp161 was replaced with Ala or Phe showed significant conformational changes on adjacent residues near the active site, particularly Gln143 and Tyr34 which in wild-type MnSOD participate in a hydrogen bond network believed to support proton transfer during catalysis. Using pulse radiolysis and observing the UV absorbance of superoxide, we have determined rate constants for the catalytic dismutation of superoxide. In addition, the rates of formation and dissociation of the product-inhibited complex of these mutants were determined by direct observation of the characteristic visible absorption of the oxidized and inhibited states. Catalysis by W161A and W161F MnSOD was associated with a decrease of at least 100-fold in the catalytic rate of reduction of superoxide, which then promotes a competing pathway leading to product inhibition. The structural changes caused by the mutations at position 161 led to small changes, at most a 6-fold decrease, in the rate constant for formation of the inhibited complex. Solvent hydrogen isotope effects support a mechanism in which formation of this complex, presumably the peroxide dianion bound to the manganese, involves no rate-contributing proton transfer; however, the dissociation of the complex requires proton transfer to generate HO(2)(-) or H2O2.

PubMed: 11580280
DOI: 10.1021/bi011047f

Experimental method

X-RAY DIFFRACTION (2.12 Å)