Viscometric, densimetric, and spectrophotometric study of lysozyme-Zn(II) and lysozyme-Hg(II) interactions

Modulation of lysozyme activity by lead administered by different routes. In vitro study and analysis in blood, kidney, and lung

Modifications in the enzyme activity of lysozyme, a protein implied in the defence barrier of the organism, can be a good biomarker of alterations in the immune system as a result of exposure to toxic metal, such as lead. The aim of this work was to evaluate the effect of a 200 ppm dose of lead on lysozyme activity in blood, kidney, and lung, and also on tissue structure. Previously, the effect of lead acetate on lysozyme activity in vitro was determined; the in vitro results indicated that lead produced a decrease in enzyme activity. The activity loss was 16 % at 200 ppm of lead. Lead acetate was administered to Wistar rats by oral and intraperitoneal injections. An increase in lysozyme activity was observed in blood when lead was administered by introperitoneal route and in kidney by the oral route. The possible immunostimulation in kidney was discarded because of the structural alterations observed in the tissue. In lung, the decrease in specific lysozyme activity, for both routes of lead exposure, seems to indicate immunosupression, which was in accordance with the structural alterations observed in this tissue.

Steady-state and time-resolved studies of the photocleavage of lysozyme by Co(III) complexes

Steady-state and time-resolved studies of site-selective photocleavage of lysozyme by cobalt(III) complexes [Co(NH(3))(5)Br](2+) and ([Co(NH(3))(4)CO(3)](+) are reported. Photocleavage resulted in two fragments of molecular masses approximately 10.5 kDa and approximately 3.5 kDa, and the yield increased (8-33%) with irradiation time (0.16-0.8 h) as well as with the metal complex concentration (0.1-5 mM). The reaction proceeded to a significant extent even when nearly stoichiometric amounts of the reagents were used. Photocleavage was effective at wavelengths ranging from 310 to 390 nm, and cleavage was inhibited by the addition of selected metal ions such as Gd(III) at moderate concentrations (2 mM). Gd(III) is known to bind at Asp52/Glu35 residues on lysozyme, and these residues are located at the enzyme active site. Current and previous studies suggest that Co(III) metal complexes bind at this site on lysozyme. Consistent with this hypothesis, [Co(NH(3))(4)CO(3)](+) (8 mM) inhibited lysozyme activity by 67%. Laser flash photolysis studies show that excitation of the metal complexes [Co(NH(3))(5)Br](2+) and ([Co(NH(3))(4)CO(3)](+) (308 nm, 20 ns pulse width) resulted in the corresponding ligand-derived radical intermediates. For example, photoexcitation of an aqueous solution of [Co(NH(3))(5)Br](2+) at 308 nm resulted in the formation of Br(2)(-*). When the excitation was carried out in the presence of lysozyme, Br(2)(-*) was quenched with a bimolecular rate constant of 1.4 x 10(9) M(-1) s(-1). Quenching resulted in protein-derived radicals (Trp(+*) and Tyr(+*)), as identified by their characteristic known transient absorption bands. Steady-state studies correlated with the time-resolved data, and taken together, these illustrated the reactivities of Co(III) metal complexes to direct protein photocleavage with high selectivity.

Effect of cadmium acetate on the conformation of lysozyme: functional implications

Structural variations of lysozyme as a consequence of its interaction with CdAc2, as well as the implications on the protein functionality have been studied. Variations in the conformation of the macromolecule are seen, however these changes are not reflected on the secondary structure. The interaction of the salt with the polypeptide chain is weak and thermodynamically unfavourable. Molecular aggregates (dimer forms) are observed at the highest salt concentrations. This interaction causes an inhibitory effect on lysozyme, the activity loss being 50% at the highest salt concentration studied. The inhibition is of mixed type with an uncompetitive component. Thus cadmium does not bind to the active site of the enzyme which is in accordance with the not very large activity loss observed. The substrate inhibition of lysozyme is favoured in the presence of the salt, so interaction with the macromolecule is at low affinity sites.

Preferential interactions in the H2O/lysozyme/AlCl3 system

The preferential interactions of lysozyme with solvent components is studied in aqueous solutions of AlCl3. The interaction parameter is negative at large salt concentrations, indicating that the interaction process of both salt and protein is thermodynamically favorable. The transfer free-energy parameter and the solubility data show that aluminum chloride is a salting-in agent for lysozyme. Moreover, these preferential interactions also are correlated with both protein solubility in the solvent medium and the influence of salt on the lysozyme structure. Viscometric and refractometric studies show that lysozyme can undergo a conformational change at 1 mM of salt, and spectrophotometric studies indicate a protein activity of approximately 75% at 10 mM of salt. Therefore, neither the interaction of AlCl3 with the lysozyme nor the conformational change undergone directly affect the catalytic amino acid residues of the active site.