Computer modelling of electron paramagnetic resonance-active molybdenum(V) species in xanthine oxidase †

Abstract

Density Functional Theory calculations have been used to investigate structural models for the ‘Very Rapid’ and ‘Inhibited’ EPR signals ascribed to xanthine oxidase Mo^V species. Analysis of the observed hyperfine coupling tensors has suggested close Mo–C contacts in both cases and a side-on interaction between the substrate’s carbonyl group and the Mo centre has been proposed. Attempts to confirm this for several model ‘Very Rapid’ species, based on a previous structure for the active site, either give short Mo–C contacts but too small a spin density on Mo or long Mo–C distances and a more reasonable Mo spin. Either the model system or the interpretation of the experimental data requires revision. In contrast, a good model can be developed for the ‘Inhibited’ species, which arises during reaction with formaldehyde, which is consistent with the EPR and other experimental data. However, rather than involving side-on co-ordination of the formaldehyde carbonyl group, the ‘Inhibited’ species forms a C–S bond between the formaldehyde and the sulfido ligand.

References

1. R. Hille, Chem. Rev., 1996, 96, 2757.
2. R. Hille, J. Biol. Inorg. Chem., 1996, 1, 397.
3. M. J. Romao, M. Archer, I. Moura, J. J. G. Moura, J. Legall, R. Engh, M. Schneider, P. Hof and R. Huber, Science, 1995, 270, 1170.
4. A. S. McAlpine, A. G. McEwan and S. Bailey, unpublished work.
5. K. Sato, H. Sasaki, A. Okubo, M. Tanokura and S. Yamazaki, Proc. Jpn. Acad., Ser. B, 1997, 73, 30.
6. H. Schindelin, C. Kisker, J. Hilton, K. V. Rajagopalan and D. C. Rees, Science, 1996, 272, 1615.
7. F. Schneider, J. Lowe, R. Huber, H. Schindelin, C. Kisker and J. Knablein, J. Mol. Biol., 1996, 263, 53.
8. R. C. Bray, B. Bennett, J. F. Burke, A. Chovnick, W. A. Doyle, B. D. Howes, D. J. Lowe, R. L. Richards, N. A. Turner, A. Ventom and J. R. S. Whittle, Biochem. Soc. Trans., 1996, 24, 99.
9. R. Hille, ACS Symp. Ser., 1993, 535, 22.
10. B. D. Howes, B. Bennett, R. C. Bray, R. L. Richards and D. J. Lowe, J. Am. Chem. Soc., 1994, 116, 11624.
11. B. D. Howes, R. C. Bray, R. L. Richards, N. A. Turner, B. Bennett and D. J. Lowe, Biochemistry, 1996, 35, 1432.
12. B. D. Howes, R. C. Bray, R. L. Richards, N. A. Turner, B. Bennett and D. J. Lowe, Biochemistry, 1996, 35, 3874.
13. B. Bennett, N. Benson, A. G. McEwan and R. C. Bray, Eur. J. Biochem., 1994, 225, 321.
14. B. Bennett, N. Benson, A. G. McEwan and R. C. Bray, Biochem. Soc. Trans., 1994, 22, S 285.
15. R. J. Greenwood, G. L. Wilson, J. R. Pilbrow and A. G. Wedd, J. Am. Chem. Soc., 1993, 115, 5385.
16. G. L. Wilson, R. J. Greenwood, J. R. Pilbrow, J. T. Spence and A. G. Wedd, J. Am. Chem. Soc., 1991, 113, 6803.
17. J. H. Kim and R. Hille, J. Inorg. Biochem., 1994, 55, 295.
18. A. G. Wedd and J. T. Spence, Pure Appl. Chem., 1990, 62, 1055.
19. A. A. Eagle, L. J. Laughlin, C. G. Young and E. R. T. Tiekink, J. Am. Chem. Soc., 1992, 114, 9195.
20. P. R. Traill, A. M. Bond and A. G. Wedd, Inorg. Chem., 1994, 33, 5754.
21. C. G. Young and A. G. Wedd, ACS Symp. Ser., 1993, 535, 70.
22. M. R. Bray and R. J. Deeth, J. Chem. Soc., Dalton Trans., 1997, 1267.
23. M. R. Bray and R. J. Deeth, Inorg. Chem., 1996, 35, 5720.
24. P. E. M. Siegbahn and R. H. Crabtree, J. Am. Chem. Soc., 1997, 119, 3103.
25. U. Ryde, M. H. M. Olsson, K. Pierloot and B. O. Roos, J. Mol. Biol., 1996, 261, 586.
26. I. G. Dance, Aust. J. Chem., 1994, 47, 979.
27. A. A. Voityuk, K. Albert, S. Kostlmeier, V. A. Nasluzov, K. M. Neyman, P. Hof, R. Huber, M. J. Romao and N. Rosch, J. Am. Chem. Soc., 1997, 119, 3159.
28. M. R. Bray, R. J. Deeth and V. J. Paget, Prog. React. Kinet, 1996, 21, 169.
29. ADF 2.3.0, Theoretical Chemistry, Vrije Universiteit, 1997.
30. G. te Velde and E. J. Baerends, J. Comput. Phys., 1992, 99, 84.
31. E. J. Baerends, D. E. Ellis and P. Ros, Chem. Phys., 1973, 2, 41.
32. J. C. Slater, Adv. Quantum Chem., 1972, 6, 1.
33. S. H. Vosko, L. Wilk and M. Nusair, Can. J. Phys., 1980, 58, 1200.
34. L. Y. Fan and T. Ziegler, J. Chem. Phys., 1991, 95, 7401.
35. L. Versluis and T. Ziegler, J. Chem. Phys., 1988, 88, 322.
36. A. D. Becke, Phys. Rev. A, 1988, 38, 3098.
37. J. P. Perdew, Phys. Rev. B, 1986, 33, 8822.
38. E. J. Baerends, D. E. Ellis and P. Ros, Theor. Chim. Acta, 1972, 27, 339.
39. T. Ziegler, Can. J. Chem., 1995, 73, 743.
40. T. Ziegler, Chem. Rev., 1991, 91, 651.
41. N. A. Turner, R. C. Bray and G. P. Diakun, Biochem. J., 1989, 260, 563.
42. R. Huber, P. Hof, R. O. Duarte, J. J. G. Moura, I. Moura, M. Y. Liu, J. Legall, R. Hille, M. Archer and M. J. Romao, Proc. Natl. Acad. Sci. USA, 1996, 93, 8846.
43. D. J. Lowe, R. L. Richards and R. C. Bray, Biochem. Soc. Trans., in the press.
44. G. N. George and R. C. Bray, Biochemistry, 1988, 27, 3603.
45. J. P. G. Malthouse, G. N. George, D. J. Lowe and R. C. Bray, Biochem. J., 1981, 199, 629.
46. R. J. Deeth, unpublished work.