Biomedical subjects

M G Pischiutta

Publications and source records attributed to M G Pischiutta.

4 recordsLinked to original sources

PubMed1987

Early conformational changes and activity modulation induced by guanidinium chloride on intestinal alkaline phosphatase.

Moderate concentrations of guanidinium chloride induce both instantaneous and time-dependent modifications of the catalytic and optical properties of intestinal alkaline phosphatase, which undergoes consecutive conformational transitions at about 0.05 M, 0.25 M and 1.0 M denaturant. A paradoxical activation is observed up to 1.0 M-guanidine, with a maximum at 0.25 M- and a mid-point around 0.5 M-guanidine. Difference absorbance and fluorescence spectra imply a change in the state of ionization of the protein residues, with variation in molecular size suggested by light-scattering. Random-coil formation is indicated by a lower fluorescence yield, a more polar environment of the aromatic residues and another separate tryptophan emission. Iodide quenching confirms the alterations of conformation. Deprotonation favours the loss of the intramolecular constraints and the enhancement of the structure disruption by guanidine.

Alkaline Phosphatase↗

PubMed1985

Ascorbic acid stability in aqueous solutions.

Different water purity provokes a great variation of the stability of ascorbic acid and isoascorbic acid solutions. The effect of temperature on ascorbate aerobic oxidation was assessed by means of Arrhenius plots from which thermodynamic parameters were derived. The presence of bovine serum albumin drastically reduces the vitamin oxidation rate regardless of stereoisomerism. On the other hand the interaction with alkaline phosphatase, an enzyme inhibited by preincubation with vitamin C, does not modify significantly the stability in the experimental conditions used.

Alkaline Phosphatase↗

PubMedDate not supplied

The kinetics of concurrent instantaneous and time dependent inhibition of alkaline phosphatase by urea and related compounds.

Urea, thiourea and guanidine-HCl greatly inhibit bone Alkaline Phosphatase activity. The inhibition displays saturation kinetics, fitting a model for the reaction sequence in which formation of complexes with increasing affinity occurs. The time dependent inactivation by urea and guanidine follows pseudo-first order kinetics, while thiourea behaviour is better described by a biexponential equation. The pH variation strongly affects the activity, the instantaneous inhibition and the time dependent inactivation. At the pH optimum the three compounds display their strongest effect. Data analysis suggests a three-stage model for the kinetics of Alkaline Phosphatase inhibition by urea and related compounds, involving a consecutive binding process with several sites of the protein and the production of different and interchanging inhibitor-enzyme complexes, leading to irreversibly inactivated forms.

Alkaline Phosphatase↗

PubMedDate not supplied

Comparison of kinetic and optical changes during guanidine denaturation of intestinal alkaline phosphatase.

The modifications of the activity of calf intestinal Alkaline Phosphatase treated with moderate amounts of guanidinium chloride are compared with the conformational changes observed by ultraviolet absorbance and intrinsic fluorescence. The time course of catalytic and optical properties of the treated enzyme develops through two distinct steps: an instantaneous and a time-dependent one. The immediate effect of guanidine is to lower emission yield, to shift the emission maximum of the enzyme to longer wavelengths and to enhance the absorbance of the protein. The rapid conformational transition determines a paradoxical activation at low effector concentration (below 0.88 M) and an inhibition at higher amounts. The following marked decay of enzyme activity with time is related to spectroscopically detectable changes. Temperature influences both kinetic and structural aspects of the process and facilitates guanidine action.

Alkaline Phosphatase↗