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West Indian med. j ; 50(suppl 7): 47, Dec. 2001.
Artigo em Inglês | MedCarib | ID: med-51


Although the enzyme cytochrome c oxidase (COX) is critical to respiration and has been studied extensively, the interactions between this enzyme and its substrate cytochrome c are still not very well understood. We employed a computer assisted approach to study these interactions. We used the Swiss-pdb v 2.5 computer programme, which measures the percentage accessibility of residues and the online server ANOLEA, which calculates the non-local energy of residues in a polypeptide chain, to analyze the respective molecular structures of cytochrome c and COX. The accessibility studies showed that, compared to the oxidized, the reduced form of cytochrome c normally had the greater proportion of more highly accessible residues: for reduced cytochrome c, 7 of the 8 residues exhibiting 55 percent accessibility were lysines. Interestingly enough, lysine 13, shown by other studies to be important for substrate binding, was not significantly accessible. For COX, neither asparate 158 nor glutamate 198 residues, reported to be important for substrate binding and catalysis, were significantly accessible either. The energy studies showed that whereas oxidized cytochrome c was a stable structure of low energy, approximatley 81 percent of the protein was reduced. For COX, a few small regions, including 4 residues in the vicinity of CuA, which functions as the enzyme's electron entry port, were of high energy. Since lysine 13, aspartate 158 and glutamate 198 are known to play important roles in enzyme-substrate interactions, it must be that these residues become more accessible when the two proteins interact. The results of the accessibility studies therefore appear to suggest that COX employs a mix of induced-fit and strain mechanisms when it binds substrate. On the basis of the energy studies, we conclude that the structure of reduced cytochrome c (the substrate) resembles a high energy transition-state intermediate and that when this protein binds and reduces oxidized COX, the structures of both proteins are stabilized. (AU)

Grupo dos Citocromos c/análise , Enzimas , Especificidade por Substrato , Complexo IV da Cadeia de Transporte de Elétrons/análise , Diagnóstico por Computador , Lisina/análise , Ácido Glutâmico/análise , Ácido Aspártico , Resíduos de Drogas/análise