PubMed Health⌕ Search

Biomedical subjects

C Cini

Publications and source records attributed to C Cini.

At least 37 records · Page 2Linked to original sources
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

Biochemical characterization of a thialysine-resistant clone of CHO cells.

The intracellular transport and the activation of lysine, thialysine and selenalysine have been investigated in a thialysine-resistant CHO cell mutant strain in comparison with the parental strain. The cationic amino acid transport system responsible for the transport of these 3 amino acids shows no differences between the 2 strains as regards its affinity for each of these amino acids. On the other hand the Vmax of the transport system in the mutant is about double that in the parental strain. The lysyl-tRNA synthetase, assayed both as ATP = PPi exchange reaction and lysyl-tRNA synthesis, shows a lower affinity for thialysine and selenalysine than for lysine in both strains; in the mutant, however, the difference is even greater. Thus the thialysine resistance of the mutant is mainly due to the properties of its lysyl-tRNA synthetase, which shows a greater difference of the affinities for lysine and thialysine with respect to the parental strain.

Adenosine Triphosphate↗
PubMed1987

Intracellular transport of thialysine and selenalysine in CHO cells.

The intracellular transport of thialysine and selenalysine in CHO cells has been studied. Data have been obtained indicating that the two lysine analogs can be transported by both the cationic aminoacid transport system and by the L transport system. The affinity of the cationic aminoacid transport system is similar for the two lysine analogs but lower than that for lysine and the affinity of the L transport system for the two lysine analogs is lower than that for leucine.

Amino Acids↗
PubMed1987

Degradation of thialysine- or selenalysine-containing abnormal proteins in CHO cells.

CHO cells can incorporate thialysine and selenalysine in their proteins in substitution of lysine. Data are reported in the present paper showing that proteins containing either thialysine or selenalysine are unstable and quite rapidly degraded. The degradation rate is strictly related to the extent of protein lysine substitution. At similar extent of substitution, selenalysine-containing proteins are more unstable that thialysine-containing ones.

Amino Acids↗
PubMed1987

Selenalysine utilization by CHO cells.

CHO cells allowed to grow in a medium containing selenalysine can utilize it for protein synthesis. Selenalysine is incorporated into cell proteins in substitution of lysine: a maximum of 5% of protein lysine can be substituted. Protein lysine substitution by selenalysine can be correlated to the reduced viability of cells grown in its presence.

Animals↗
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↗
PubMed1984

Transport of basic aminoacids in E. coli.

Two transport systems for ornithine and one for arginine have been evidenced in E. coli KL16. The transport system for arginine is quite specific whereas the two for ornithine show a poor specificity. Citrulline and arginine non competitively inhibit ornithine transport. They show homotropic cooperativity and synergic inhibitory effect.

Amino Acids↗
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↗
PubMed1983

Repression of lysine transport in E. coli KL16.

Data reported in this paper show that both lysine transport systems in E. coli KL16 can be repressed by lysine and its isologs, thialysine and selenalysine, whereas they are not repressed by ornithine. The repression is specific on lysine transport systems; it is evident with 0.01 mM lysine or isolog concentration and reaches a maximum with 0.1 mM concentration. By comparing the extent of repression by lysine and its isologs, lysine gives the highest and selenalysine the lowest degree of repression. The shift from the repressed to the depressed state is rather immediate once the amino acid is removed from the culture medium.

Biological Transport↗
PubMed1982

Thialysine utilization by E. coli and its effects on cell growth.

Thialysine can be utilized for growth by a wild type K12 strain of E. coli. It is incorporated into proteins in substitution and in competition with lysine; up to 17% of protein lysine can be substituted by thialysine. Nevertheless the presence of thialysine in the culture medium gives rise to an inhibition of cell growth rate. This effect has been correlated to the inhibition of protein synthesis rate by thialysine and to the extent of protein lysine substitution by the analog. On the other hand this substitution does not affect cell viability.

Bacterial Proteins↗
PubMed1982

Selenalysine utilization for growth and protein synthesis by a lysine requiring E. coli mutant.

Selenalysine can be utilized in substitution of lysine by a lysine requiring E. coli mutant. The presence of some lysine in the culture medium is necessary to allow selenalysine utilization for growth; in the presence of an excess of lysine, selenalysine is not utilized. When utilized, selenalysine gives rise to an increase of final growth. However, it shows some toxic effects as demonstrated by the decrease of both growth rate and cell viability. Selenalysine is incorporated into proteins in substitution of lysine. Up to a maximum of 50% of total protein lysine can be substituted. The decrease of cell viability is correlated with the extent of lysine substitution.

Cell Division↗
PubMed1981

In vivo incorporation of selenalysine in Escherichia coli proteins and its effects on cell growth.

The presence of selenalysine in the culture medium at concentration ranging from 0.05 to 0.3 mM inhibits Escherichia coli growth rate and cell viability. The inhibition of cell growth rate can be imputed to the inhibition of protein synthesis and can be only partially reverted by lysine. Selenalysine is incorporated into cellular proteins in substitution of and in competition with lysine, reaching the value of about 1% as molar fraction with respect to the total amino acids, and substituting up to 14% of protein lysine. The effect of selenalysine on cell viability can be correlated to the extent of its incorporation into proteins, and can be completely reverted by lysine. However, substitution up to 5% of protein lysine by selenalysine does not affect the viability, thus indicating that some degree of substitution can be well tolerated by the cell.

Bacterial Proteins↗
PubMed1980

Beta-selenaproline as competitive inhibitor of proline activation.

Beta-Selenaproline, a proline analog having the beta-methylene group substituted by a selenium atom, has been tested in ATP-PPi exchange reaction catalyzed by either Escherichia coli or rat liver aminoacyl-tRNA synthetases. It has been shown that with both enzymatic systems beta-selenaproline does not give rise to ATP-PPi exchange, but specifically inhibits proline activation. The inhibition is of fully competitive type and the Ki values, lower than the Km values for proline, show that beta-selenaproline binds to the synthetases with high affinity. The inability to form the complex with AMP, taking into account also the behavior of gamma-selenaproline and other proline analogs, has been ascribed to the presence of the selenium atom in the beta-position.

Adenosine Triphosphate↗