Metal complexes of non-heme ligands: biological applications

<p>Oxidative inactivation of proteins (carbonic anhydrase–I, trypsin, chymotrypsin and 20S proteasome) by non–heme iron complexes, and glutathionylation of non–heme cobalt complexes mimicking the N5 coordination environment like that of biologically important cofactor cobalamin or B₁₂ (Cbl) are reported. Different non–heme ligand sets or inhibitors were used to inactivate different proteins. Carbonic anhydrase–I (CA–I) and 20S proteasome were inactivated by iron complexes in the presence of O₂ and a reductant (DTT), consistent with a pathway involving the reductive activation of O₂, whereas serine proteases trypsin and chymotrypsin were inactivated by ferryls (single turnover), and by an iron complex in presence of biologically relevant oxidant, H₂O₂ (catalytic conditions). Analysis of the CA–I inactivation products by SDS–PAGE, ESI–MS and LC/MS/MS confirmed that the protein is inactivated by oxidation of amino acid side chains (His, Trp and Met) rather than fragmentation of the protein backbone. On the other hand, amino acid analysis of serine proteases inactivation products confirmed that residues Cys, Tyr, and Trp were oxidized under single turnover condition while the residue tyrosine was oxidized selectively under catalytic conditions. Control experiments preclude the role of ROS, and supported the role of a metal-based oxidant responsible for protein inactivation in all the cases.</p> <p>A low spin cobalt (III) cobalamin model complex derived from a polypyridyl pentadentate N5 non–heme ligand was synthesized and characterized fully by X–ray crystallography, UV–vis, IR, ¹H–NMR and ¹³C–NMR spectroscopies, and mass spectrometry (HRMS). Kinetic and thermodynamic studies on the reaction of this cobalt complex along with another related congener with glutathione were performed in aqueous buffer to generate biomimetic species of glutathionylcobalamin, an important form of cobalamin found in nature. The reaction follows second order kinetic, with both the rate constants and the observed equilibrium constants smaller than the rate constants and equilibrium constant of the reaction of aquacobalamin and GSH to give glutathionylcobalamin. Glutathionylation showed significant pH dependence, where rates increased with pH. Taken together, these results suggest that glutathionylation is a general reaction for Co(III) complexes related to Cbl.</p>

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Open Access Dissertation

Discipline thesis:degree_discipline

Chemistry

Year dc:date.available

2012

Author dc:creator

• Prakash, Jai

Contributors dc:contributor

• Jeremy J. Kodanko

• Chemistry

Repository record dc:identifier

https://digitalcommons.wayne.edu/oa_dissertations/518

OAI identifier oai:identifier

oai:digitalcommons.wayne.edu:oa_dissertations-1517