Maria Benedetta Fadda

New halogenated phenylcoumarins as tyrosinase inhibitors

With the aim to find out structural features for the tyrosinase inhibitory activity, in the present communication we report the synthesis and pharmacological evaluation of a new series of phenylcoumarin derivatives with different number of hydroxyl or ether groups and bromo substituent in the scaffold. The synthesized compounds 5-12 were evaluated as mushroom tyrosinase inhibitors showing, two of them, lower IC(50) than the umbelliferone. Compound 12 (IC(50)=215 μM) is the best tyrosinase inhibitor of this series.

Circadian rhythms of histatin 1 histatin 3, histatin 5, statherin and uric acid in whole human saliva secretion

The circadian rhythms of histatins 1, 3, 5, of statherin and uric acid were investigated in whole human saliva. Histatins showed a rhythm approximately synchronous with salivary flow rate (acrophase around 5 pm), the higher amplitude pertaining to histatin 1 (about 50% of the mesor). Uric acid showed a large rhythm asynchronous with flow rate and histatin concentrations (4.4 ± 1.4 am). Statherin did not show a significant circadian rhythm on five of six volunteers. This finding confirms that the secretion route of statherin is different from that of histatins.

Synthesis and biological evaluation of a novel series of bis-salicylaldehydes as mushroom tyrosinase inhibitors.

A series of novel bis-salicylaldehydes were synthesised and evaluated as tyrosinase inhibitors using a tyrosinase-dependent L-DOPA oxidation assay. The bis-salicylaldehydes exhibited greater inhibitory activity than salicylaldehyde. Our data suggests that these novel compounds may serve as a structural template for the design and development of novel tyrosinase inhibitors.

Highly efficient solubilization of natural lignocellulosic materials by a commercial cellulase immobilized on various solid supports

SummaryA commercial preparation of cellulase was immobilized on CNBr-sepharose, ConA-sepharose, and CNBr-glass beads. When filter paper was used as the substrate, the specific activity of the enzyme immobilized on ConA-sepharose was more than twice that of the soluble enzyme, while the activity of the enzymes immobilized on the other two substrates was either very slightly (CNBr-sepharose) or slightly (CNBr-glass beads) reduced. The immobilized enzymes showed alterations both in the Km and V max values: these were generally either slightly increased (Km) or reduced (V max). In addition, the immobilized enzymes were more resistant to inhibition both by glucose and cellobiose, they were all more stable than the soluble enzyme and solubilized three different natural lignocellulosic materials (alfa-alfa, wheat straw, and pine needles) to a much greater or significantly greater extext than the soluble enzyme: the ConA-sepharose cellulase was the most efficient. The possibility of reusing the immobilized enzyme was also tested. It was found that the ConA-sepharose cellulase could be reused five times with a final loss of activity that ranged between 30% and 50%.

Benthic mucilagenous aggregates: Biochemical characterization and ligand binding properties

Abstract The biochemical composition of benthic mucilaginous aggregates collected from the south-western coastal waters of Sardinia in the Mediterranean Sea was analysed. Acidic glycoproteins surrounding the included microorganisms, mainly diatoms, were found to be the predominant fraction. The aggregates, diluted and finely dispersed by ultrasonic treatment, bound with ammoniated ruthenium oxychloride (ruthenium red), a specific ligand for the acidic glycoproteins. When concentrated crude aggregates were used, ruthenium red was bound both chemically and by physical entrapment. The data were consistent with the Langmuir ligand binding isotherm. The extent of physical adsorption displayed a clear pH dependence. Physical adsorption was predominant at acidic pH, suggesting that the stabilization of the supramolecular structure of the aggregates also depends on the degree of protonation of the acidic glycoresidues. A structural model of the aggregates is proposed, where the mucus matrix containing acidic binding sites acts as an intercellular glue, providing a molecular sieve-like filtering capacity to the aggregates dispersed in seawater.

A new synthetic polymer as a support for enzyme immobilization

Abstract A method for the preparation and derivatization of an acrylic polymeric support and some topochemical reactions are described here. The support was also found to be effective to immobilize enzymes.

Tyrosine-like condensed derivatives as tyrosinase inhibitors

Objectives  We report the pharmacological evaluation of a new series of 3‐aminocoumarins differently substituted with hydroxyl groups, which have been synthesized because they include in their structures the tyrosine fragment (tyrosine‐like compounds), with the aim of discovering structural features necessary for tyrosinase inhibitory activity.

A highly active fungal β-glucosidase - Purification and properties

A highly active thermostable β-glucosidase was purified to homogeneity from a strain ofTrichoderma sp. The enzyme was an extracellular glycoprotein and showed hydrolytic activity toward several β-glucosides.Cellobiose was found to be the substrate of choice for this enzyme. This finding could suggest future technological applications of the purified protein.

Inhibition of diamine oxidase by antihistaminic agents and related drugs.

Various drugs were tested as inhibitors of diamine oxidase on the basis of chemical relationships to the enzyme substrates.It was found that serotonine tryptamine and phenformin are good competitive inhibitors while cimetidine and pheniprazine are non-competitive inhibitors. Other antihistaminic drugs like promethazine are less powerful inhibitors.

Selective inactivation of catalase during protoporphyrin induced photohemolysis of human red blood cells

The level of some enzymatic activities in red blood cells before and after photohemolysis induced by protoporphyrin IX was studied. A 30% decrease in catalase activity was found both in normal erythrocytes and those from patients affected by favism. Other proteins though present in larger amounts inside the erythrocytes are not affected by the photohemolytic process.