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Biomedical subjects

R Santus

Publications and source records attributed to R Santus.

157 records · Page 9Linked to original sources
PubMed1975

The role of metal ions in the radiosensitivity of metalloproteins. Model experiments with bovine carbonic anhydrase.

The radiation-induced inactivation of dilute solutions of three forms of bovine carbonic anhydrase (metal-free apo-BCA, Zn2+-BCA and Co2+-BCA) has been studied. The presence of the metal ions did not alter the sensitivity of the enzyme to inactivation by oxidizing radicals; however, they exerted a protective effect against inactivation by reducing radicals. Data obtained using the amino-acid-specific inorganic radical anions (CNS)2-and Br2-allowed the identification of histidine, tyrosine and tryptophan as residues essential to the activity of bovine carbonic anhydrase when assayed by p-nitro-phenylacetate.

Carbonic Anhydrases↗
PubMedDate not supplied

Structure-activity relationship of macrocyclic and linear gadolinium chelates: investigation of transmetallation effect on the zinc-dependent metallopeptidase angiotensin-converting enzyme.

Transmetallation between commercially available solutions of gadolinium (Gd) chelates and the zinc (Zn)-dependent angiotensin-converting enzyme (ACE) was investigated. In vitro, the strongest inhibitions were observed for the linear Gd complexes, Gd diethylenetriamine pentaacetic acid (DTPA) bis-methylamide (BMA) (IC50 = .016 +/- .006 mmol/l) and Gd-DTPA (IC50 = .350 +/- .034 mmol/l). The two macrocycles Gd tetraazacyclododecane tetraacetic acid (DOTA) and Gd-HP-DO3A were similar and 400 times less active than Gd-DTPA-BMA. These effects were mainly due to the presence of free ligand for DTPA and calcium (Ca) chelate in the case of DTPA-BMA because the addition of Zn2+ in the same quantities suppresses their inhibitory effects. In vivo, these two solutions of linear Gd chelates significantly inhibited ACE activity (Gd-DTPA: (67 +/- 9% versus baseline; and Gd-DTPA-BMA: 73 +/- 2% versus baseline at the clinical dose of .1 mmol/kg), whereas no significant effect was observed for the two macrocyclic chelates Gd-DOTA and Gd-HP-DO3A. Formulating the Gd chelate solution with either an excess of free ligand or Ca chelate (to decrease Gd3+ release) in the case of linear Gd chelate may have deleterious biologic consequences.

Chelating Agents↗
PubMedDate not supplied

[Mechanism of quenching of hematoporphyrin and mono-L-aspartyl chlorine e6 triplet states by metronidazole].

The quenching of the triplet state of hematopophyrin (3HP.) and mono-L-aspartyl chlorine e6, (3MACE.) by metrotlidazole (METRO) ground state, has been investigated in binary mixtures of water and aliphatic alcohol by means of 532 nm laser flash. In water, both 3HP. and 3MACE. quenched by METRO with at rate: kQw = 1.9 x 10(9) M-1.s-1. The quenching is accompanied by the appearance of a transient absorbance near 690 nm. This transient absorbance corresponds to the tetrapyrrole radical-cation formation in result of an electron transfer between 3HP. or 3MACE. and METRO. In neat alcohol, the electron transfer was not observed. In binary mixtures the quenching constant is reduced as the molar fraction of water is decreased. In water, the activation barrier of the quenching is 5.9 kcal/mol for HP and 3.9 kcal/mol for MACE. In going from water to water-alcohol mixtures the energy of activation is practically unchanged. Based on flash photolysis data, and analysis of absorption spectra of METRO we conclude that the electron-acceptor ability of metronidazole essentially depends on the intermolecular interaction with nearby solvent molecules. The mechanism of the quenching is discussed.

Electron Transport↗