title: Analogues containing the paramagnetic amino acid TOAC as substrates for angiotensin I-converting enzyme.
abstract: The angiotensin I-converting enzyme (ACE) converts the decapeptide angiotensin I (Ang I) into angiotensin II by releasing the C-terminal dipeptide. A novel approach combining enzymatic and electron paramagnetic resonance (EPR) studies was developed to determine the enzyme effect on Ang I containing the paramagnetic 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC) at positions 1, 3, 8, and 9. Biological assays indicated that TOAC(1)-Ang I maintained partly the Ang I activity, and that only this derivative and the TOAC(3)-Ang I were cleaved by ACE. Quenching of Tyr(4) fluorescence by TOAC decreased with increasing distance between both residues, suggesting an overall partially extended structure. However, the local bend known to be imposed by the substituted diglycine TOAC is probably responsible for steric hindrance, not allowing the analogues containing TOAC at positions 8 and 9 to act as substrates. In some cases, although substrates and products differ by only two residues, the difference between their EPR spectral lineshapes allows monitoring the enzymatic reaction as a function of time.
authors.affiliation: Department of Biophysics, Universidade Federal de Sao Paulo, Rua Três de Maio 100, 04044-020 Sao Paulo, Brazil.
authors.forename: Luis Gustavo
authors.initials: LG
authors.lastname: de Deus Teixeira
authors.forename: Patrícia Alessandra
authors.initials: PA
authors.lastname: Bersanetti
authors.forename: Shirley
authors.initials: S
authors.lastname: Schreier
authors.forename: Adriana Karaoglanovich
authors.initials: AK
authors.lastname: Carmona
authors.forename: Clovis Ryuichi
authors.initials: CR
authors.lastname: Nakaie
mesh_terms: D000818:Animals; D003497:Cyclic N-Oxides / Q000737:chemistry / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D005260:Female; D006168:Guinea Pigs; D007082:Ileum / Q000201:enzymology; D007700:Kinetics; D013058:Mass Spectrometry; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D007703:Peptidyl-Dipeptidase A / Q000378:metabolism*; D051381:Rats; D013050:Spectrometry, Fluorescence; D013379:Substrate Specificity; D014599:Uterus / Q000201:enzymology
chemical_list: D003497:Cyclic N-Oxides; D010455:Peptides; D007703:Peptidyl-Dipeptidase A; C037109:2,2,6,6-tetramethylpiperidine-N-oxide-4-amino-4-carboxylic acid