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R Coccia

Publications and source records attributed to R Coccia.

At least 37 records · Page 2Linked to original sources
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

Aspartokinase III repression and lysine analogs utilization for protein synthesis.

The extents of thialysine and selenalysine incorporation into cell proteins were compared in E. coli KL16 and in a mutant able to grow equally well in the presence or in the absence of both lysine analogs. The mutant differs from the parental strain in the repression of aspartokinase III (AKIII), the first enzyme of the lysine biosynthetic pathway. No analog incorporation into proteins was observed in mutant cells grown in the presence of either analog, whereas a marked analog incorporation was observed in the parental strain, where up to 17% and 12% of protein lysine can be substituted by thialysine and selenalysine respectively. In the parental strain grown in media containing either analog at different concentration the extent of analog incorporation into proteins is related to the extent of AKIII repression.

Aspartate Kinase↗
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↗
PubMed1989

Selenalysine transamination by a bovine brain enzyme.

Selenalysine is deaminated by glutamine transaminase from bovine brain, leading to the production of the corresponding alpha-ketoacid, which spontaneously cyclizes to a ketimine form. Selenalysine shows a good affinity for the enzyme.

Animals↗
PubMed1988

Oxidative deamination of Se-(1-carboxyethyl)-,Se-(1-carboxypropyl)- and Se-(2-carboxyethyl)-selenocysteine by snake venom L-aminoacid oxidase.

Details are reported for the synthesis of Se-(1-carboxyethyl)-selenocysteine (1-CESeC), Se-(1-carboxypropyl)-selenocysteine (1-CPSeC) and Se-(2-carboxyethyl)-selenocysteine (2-CESeC). They can be obtained in pure cristalline form with good yield. Some chromatographic properties, useful for their identification, are described. The three aminoacids are good substrates for snake venom L-aminoacid oxidase, giving the corresponding alpha-ketoacids as reaction products.

Amino Acid Oxidoreductases↗
PubMed1988

Degradation of thialysine- or selenalysine-containing abnormal proteins in E. coli.

Thialysine and selenalysine can be utilized for protein synthesis by lysine-requiring E. coli cells even in the absence of lysine. Protein synthesis has been determined as labeled leucine incorporation into acid-insoluble material, as increase of cell proteins and as protein-lysine substitution by the analog. Either analog can be incorporated into proteins, in the absence of lysine, for a limited time interval after which cells stop to duplicate. Proteins synthesized during this period contain most of their lysine residues substituted by the analog. Moreover, it has been shown that the analog-containing proteins are unstable and rapidly degraded. Their instability would account for the inability of lysine-requiring E. coli cells to utilize the analog as growth factor.

Bacterial Proteins↗
PubMed1988

Thialysine- and selenalysine-resistance in a E. coli mutant.

A thialysine-resistant mutant of E. coli strain KL16 also shows a lower sensitivity to selenalysine, the lysine analog containing selenium. No difference between the mutant and the parental strain has been shown regarding the affinities of the transport systems and the lysyl-tRNA synthetase for selenalysine, thialysine and lysine as well as the inhibitory effects of these three aminoacids on the activity of the lysine biosynthetic pathway. A marked difference between the two strains has been evidenced in the AK III repression: in the mutant the repression by selenalysine, thialysine and lysine is much lower than in the parental strain.

Aspartate Kinase↗
PubMed1987

Recognition of aminoethylhomocysteine and aminopropylcysteine by aminoacid transport systems and aminoacyl tRNA synthetases.

In E. coli aminoethylhomocysteine (AEHC) and aminopropylcysteine (APC) do not affect intracellular lysine transport thus showing that they cannot bind the E. coli lysine transport systems. In CHO cells AEHC and APC inhibit lysine and arginine transport, AEHC more than APC, thus indicating that they can bind the cationic aminoacid transport system. They inhibit also leucine transport, APC more than AEHC. Some possible relationships between their structure and their effects on transport systems are considered. AEHC and APC are not activated by aminoacyl-tRNA synthetase preparations from bacterial and mammalian sources.

Amino Acids↗
PubMed1986

Effects of selenalysine on CHO cells.

Selenalysine, the lysine isolog with the 4-methylene group substituted by a Selenium atom, inhibits growth rate and plating efficiency of Chinese Hamster Ovary (CHO) cells. It does not affect DNA and RNA synthesis, but inhibits protein synthesis. Cells grown in the presence of selenalysine show a reduced viability and an increased cell volume. Almost all the effects of selenalysine on CHO cells can be reversed by lysine, thus indicating that selenalysine acts mainly in competition with lysine by impairing its utilization.

Animals↗
PubMed1986

Effects of selenalysine on thialysine resistant CHO cells.

A thialisyne resistant variant clone of CHO cells also shows a lower sensitivity to selenasyne, the lysine analog containing selenium. Growth rate, cell viability and protein synthesis rate are less affected by selenasyne in the variant compared to the parental strain. Data are reported showing that during cellular growth of either strain some toxic derivatives of selenasyne are produced and accumulated in the culture medium even in the presence of excess lysine.

Animals↗
PubMed1986

Thialysine utilization for protein synthesis by CHO cells.

Chinese Hamster Ovary (CHO) cells utilize thialysine when added to the culture medium. Thialysine utilization is prevented by increasing lysine concentration in the medium, thus indicating that thialysine is utilized in substitution for and in competition with lysine. Almost all thialysine disappeared from the medium is recovered in cell protein hydrolysates. Thialysine is used for protein synthesis in substitution for lysine, and up to 10% of lysine can be substituted.

Amino Acids↗
PubMed1986

Thialysine utilization by thialysine resistant CHO cells.

Thialysine resistant CHO cells utilize thialysine added to the culture medium to a lesser extent than the parental cells. Thialysine is utilized in protein synthesis and it is incorporated into proteins in place of lysine. The parental strain substitutes up to 11% of protein lysine by thialysine, while variant cells substitute a maximum of 5% of protein lysine.

Amino Acids↗
PubMed1985

Effects of thialysine on CHO cells growth.

Thialysine, the lysine isolog with the 4-methylene group substituted by a sulfur atom, inhibits the growth rate and plating efficiency of Chinese Hamster Ovary (CHO) cells. The inhibition can be reversed by lysine, when added to the culture medium together with thialysine or shortly after; to have a complete reversion a lysine concentration five times that of thialysine is necessary. Cells grown in the presence of thialysine show a decreased viability and an increased volume. Thialysine inhibits protein synthesis, while it does not affect DNA and RNA synthesis. Protein synthesis inhibition can be reversed by lysine. Overall the results obtained indicate that thialysine affects cellular functions by impairing lysine utilization.

Animals↗
PubMed1985

The conversion of L-cystathionine into the cyclic ketimine form by heated rat liver extracts containing cystathionase and transaminase activities.

Rat liver homogenates heated for 10 min at 60 degrees C incubated with L-cystathionine yield cystathionine ketimine which was identified by its typical UV spectrum and by cochromatography with authentic samples on the amino acid analyzer. Alanine and alpha-amino butyric acid have been also detected among the final products. The reaction is due to heat stable gamma-cystathionase and transaminases present in the extracts. Cystathionase produces alpha-keto butyric acid and pyruvic acid which are then used for the transamination of the remaining cystathionine to yield the ketimine. This is the first report indicating the occurrence in a mammalian tissue of an enzymatic system using cystathionine for reactions differing from the traditional transulfuration to cysteine.

Animals↗
PubMed1984

Thialysine utilization by a lysine-requiring Escherichia coli mutant.

Thialysine cannot completely substitute lysine as growth factor for a lysine-requiring E. coli mutant. However it can be utilized for growth in the presence of limiting amounts of lysine, in substitution of, and in competition with this latter. The effects of thialysine on growth rate, protein synthesis rate and cell viability, and its incorporation into proteins were studied in function of lysine and thialysine concentration in the culture media. Up to 60% of protein lysine substitution by thialysine is observed, without appreciable effects on cell viability.

Bacterial Proteins↗
PubMed1983

Transport systems for lysine, thialysine and selenalysine in E. coli KL16.

Two lysine transport systems have been identified in E. coli KL16. They differ in their affinity for lysine, one showing a KM of 0.36 microM and the other a KM of 4.7 microM. Different compounds with chemical similarities to lysine were tested for their capacity to interfere with lysine transport. Among these only thialysine and selenalysine competitively inhibit lysine transport. The inhibition is on both transport systems. Thialysine shows a KI of 4 microM for the low affinity system and a KI of 8 microM for the high affinity system. Selenalysine shows values of 6 microM and 12 microM respectively.

Biological Transport↗