PubMed Health⌕ Search

Biomedical subjects

M A Rosei

Publications and source records attributed to M A Rosei.

At least 37 records · Page 2Linked to original sources
PubMed1994

Some biochemical properties of melanins from opioid peptides.

Opioid peptides are converted by mushroom tyrosinase into melanin-like compounds retaining the peptide moiety (opio-melanins). Opio-melanins, owing to the presence of the linked aminoacids and in contrast with DOPA-melanin, are soluble compounds. The enkephalin-generated melanins are cleaved by carboxypeptidase A and pronase whereas aminopeptidase M cannot remove aminoacids from the pigment. Enkephalins, as well as other opioid peptides, (alpha-endorphin, kyotorphin, esorphins) if oxidized in presence of DOPA and tyrosinase are readily incorporated into DOPA-melanin. The resulting mixed-melanins (opio-melanin + DOPA-melanin) can be solubilized in hydrophilic solvents. Melanin from leu-enkephalin exhibits paramagnetism as evidenced by an EPR spectrum identical to that of DOPA-melanin, but unlike the latter pigment, it does not appear to oxidize NADH, probably for the presence of the peptide moiety that exerts a hampering effect on the oxidizing capacity.

Amino Acid Sequence↗
PubMed1992

Melanins production from enkephalins by tyrosinase.

Leu-enkephalin and Met-enkephalin are oxidized in vitro by mushroom and sepia tyrosinase giving rise to synthetic melanins whose production is dependent on incubation time and on enzyme concentration. The Enk-melanins formed are acid-insoluble brownish or reddish pigments showing a continuous absorbance in the visible region when dissolved in basic solution. The presence of the amino acid chain makes them fully soluble in pH 7.4 0.05 M phosphate buffer and methanol.

Amino Acids↗
PubMed1991

The peroxidase-catalyzed oxidation of enkephalins.

In vitro experiments are reported showing that Leu-enkephalin and Metenkephalin, in the presence of hydrogen peroxide, can be oxidized by horseradish peroxidase. The products formed are strongly fluorescent and characterized by absorption peaks with maxima at 290 nm and 315 nm. The effects of substrate and enzyme concentrations on the oxidation rate of enkephalins are described. Amino acid analysis of the hydrolysates from peroxidase-treated enkephalins provides evidence for the presence of dityrosine. The data suggest that the oxidation leads to the production of enkephalin dimers with a linkage between the N-terminal tyrosine residues. Data are also obtained indicating that enkephalins function as hydrogen donors for mammalian peroxidases.

Chromatography, High Pressure Liquid↗
PubMed1991

The peroxidase-catalyzed oxidation of kyotorphins.

In vitro experiments are reported showing that the dipeptides Tyr-L-Arg (kyotorphin) and Tyr-D-Arg (D-Arg-kyotorphin) can be oxidized by H2O2-horseradish peroxidase system: the products formed are characterized by absorption spectra with two peaks at 290 nm and 315 nm. The effects of substrate and enzyme concentration on the oxidation rate are described. Amino acid analysis of hydrolysates of peroxidase-treated kyotorphins provides evidence for the presence of dityrosine. The data suggest that the oxidation leads to the production of dimers with an o,o-linkage between the tyrosine residues.

Amino Acids↗
PubMed1990

Biochemical and immunological studies of deglycosylated Rhus vernicifera laccase.

Rhus vernicifera laccase (Japanese) was deglycosylated by treating it with exo- and endoglycosidases. In absence of unfolding agents deglycosylation does not exceed 32% while in denaturating conditions only 10% of saccharides are not digested. In the former case specific activity seems to be directly related to the amount of the residual carbohydrates. After deglycosylation in denaturing conditions the modified enzyme exhibits an electrophoretic component of about 60-65 Kd. A stabilizing effect of saccharide moiety on the catalytic site of native laccase was demonstrated. Antiserum raised against the enzyme recognized native Japanese, Vietnamese as well as deglycosylated laccase indicating that the two isoforms are immunologically similar.

Antigen-Antibody Complex↗
PubMed1989

Enkephalins and exorphins oxidation by tyrosinase.

Tyrosinase activity was tested on some tyrosine-containing peptides (enkephalins and exorphins). All they are substrates for tyrosinase, showing a good affinity for the enzyme, in some cases higher than tyrosine itself. Aminoacid analysis after hydrolysis of long-lasting incubation mixtures of tyrosinase with Leu-enkephalin in presence of reductants demonstrates the formation of DOPA. The production of a new peptide containing DOPA derived from the oxidation of Leu-enkephalin was revealed by high performance liquid chromatography (HPLC).

Amino Acid Sequence↗
PubMed1987

Inhibition of Dopa decarboxylase by caffeic acid and related compounds: structure-activity relationships.

The inhibition of purified Dopa decarboxylase, has been performed with dihydroxyphenyl derivatives devoided of the NH2 group and unable to form the Schiff base with pyridoxal-5' phosphate. The more efficient inhibition is displayed by caffeic acid and related compounds that present an insaturation in the chain. The relative contribution to the inhibition by the chain and ring structures has been evaluated.

Aromatic Amino Acid Decarboxylase Inhibitors↗
PubMed1984

Oxygraphic assay of 3,4-dihydroxyphenylalanine decarboxylase activity by coupled reaction with free and immobilized serum amine oxidase.

An oxygraphic method for the assay of 3,4-dihydroxyphenylalanine (Dopa) decarboxylase activity which makes use of the coupled reactions of Dopa decarboxylase with serum amine oxidase is presented. Both free and immobilized amine oxidases were utilized. The assay is simple, rapid, and allows a continuous monitoring of the reaction. The kinetic parameters for Dopa decarboxylase obtained with the coupled assay do not significantly differ from those obtained by standard methods.

Amine Oxidase (Copper-Containing)↗
PubMed1982

Inhibitors binding to L-aromatic amino acid decarboxylase.

The effect of a number of inhibitors of L-aromatic amino acid decarboxylase activity on the absorption spectrum of the enzyme-bound coenzyme has been studied. It has been observed that the compounds tested, even if devoid of the amino function and therefore unable to form the Schiff base with the coenzyme, modify significantly the enzyme spectrum, indicating their binding to the coenzyme active site. Spectral modifications suggest that at least two kinds of binding of inhibitors to L-aromatic amino acid decarboxylase may occur, depending on their structural features. Moreover, from the spectra obtained at different concentrations of the inhibitors their affinity constants have been determined: data indicate that the cathecol ring gives the largest contribution to the binding, while the presence of the carboxyl group, the aminic group and the aliphatic chain are responsible for a decrease in the binding, which could be relevant for the efficiency of the catalysis.

Aromatic Amino Acid Decarboxylase Inhibitors↗