Mechanistic investigation of dinuclear peptidase from Streptomyces griseus and Alteromonas sp. by using alternative catalysis: Transition-state analogue substrates as probes
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- Tez No: 403287
- Danışmanlar: Prof. LI-JUNE MING, Prof. STEVEN H. GROSSMAN
- Tez Türü: Doktora
- Konular: Kimya, Chemistry
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2003
- Dil: İngilizce
- Üniversite: Unıversıty Of South Florıda
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: Belirtilmemiş.
Özet
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Özet (Çeviri)
Streptomyces (sAP) and Alteromonas prolidase (aspP) require two equivalents of metal ions for full activity and have been reported to catalyze alternative reactions, i.e., hydrolysis of phosphodiester and phosphotriester, respeetively. sAP is specific toward hydrolysis of peptides with a hydrophobic amino acid at the N-terminus, while aspP is specific toward didpeptides with a proline residue at the C-terminus. Kinetic investigations of metal derivatives ofsAP toward the hydrolysis of peptide and phosphoesters reveal mechanistic differences. For example: (a) Two protons are in-flight at the rate-determining step in peptide hydrolysis but one proton in phosphoester hydrolysis.(b) Fluoride uncompetitively inhibits peptide hydrolysis by sAP but does not inhibit phosphodiester hydrolysis, reflecting that the generation of nucleophile in these reactions are different. Fluoride inhibition of the hetero-dinuclear derivatives MnM-sAP (M = Mn2+, Co2+, Ni2+, Zn2+, and Cd2+) shows that the nucleophile is influenced by both metal, but predominantly the“second metal”, (d) Comparison of the results for Leu-pNA hydrolysis by metal derivatives of sAP shows that the kcat value is controlled by the second metal. On the other hand phosphodiester hydrolysis seems to be controlled by both metals suggesting bridging biııding mode of substrate. (e) Phosphate competitively inhibits phosphodiester hydrolysis while noncompetitively inhibiting peptide hydrolysis. (f) The pH profiles of the rate constants of these substrates reveal different iomzable groups in the reaction, particularly the N-terminal amino group of peptide substrates. Based on the results presented in this dissertation, the mechanism for hydrolyses of peptide and phosphoester by sAP are proposed. Kinetic investigations of asp? toward hydrolysis of Leu-Pro and p-nitrophenyl soman (pNPS) reveal some details about the mechanism of these reactions. (a) Nucleophiles are the same for the hydrolysis of Leu-Pro and pNPS. (b) Hydrolysis of Leu-Pro by asp? has a smaller pH window than pNPS hydrolysis, which may result from the deprotonation of the amino group in peptide substrate at ~ pH 8.0. (c) The catalytic efficiency oî asp? toward the hydrolysis of Leu-Pro is controlled by substrate binding, possibly involving the active-site His residue. Here, the mechanism for hydrolysis of Leu-Pro and pNPS by asp? are proposed based on the kinetic studies.
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