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Biomedical subjects

F Naider

Publications and source records attributed to F Naider.

At least 127 records · Page 7Linked to original sources
PubMed1979

Peptidase activities in Saccharomyces cerevisiae.

At least four distinct aminopeptidase activities and a single dipeptidase activity were found in cell extracts of a leucine-lysine auxotroph of Saccharomyces cerevisiae. The assay for peptidase activity involved polyacrylamide gel electrophoresis followed by an enzyme-coupled activity staining procedure. The aminopeptidases had largely overlapping specificities but could be distinguished from one another by their electrophoretic mobilities and activities toward different peptide substrates. Substrates tested included both free and blocked di- and tripeptides and amino acid derivatives.

Amino Acids↗
PubMed1979

The preferred conformations of protected homodito homoheptamethionine peptides. A1 H n.m.r. study in deuterochloroform medium.

Detailed analyses of the conformations of the homo-oligopeptide series, Boc-(L-Met)n-OME n = 2--7, in deuterochloroform have been carried out with proton n.m.r. and IR spectroscopy. Well-resolved high field n.m.r. spectra with assignments for the NH and alpha-CH resonances of these homo-methionine peptides are presented. Extensive n.m.r. concentration-dependent chemical shift studies are combined with IR results to delineate the involvement of the various methionine NH protons in intra- and/or intermolecular hydrogen bonding. N.m.r. chemical shift dependencies with temperature and solvent, DMSO-d6, are used to explore the strength of the hydrogen bonds for the various oligopeptides. At low concentrations, where peptide aggregation is absent, the dipeptide is found to be disordered. The tetra- to heptapeptides possess intramolecular hydrogen bonded seven-membered rings at internal residues. The number of internal rings and the oligopeptide self-association increase with increasing peptide chainlength. At intermediate concentrations associations of peptide molecules with folded structures occur with initial association at the C-terminal region. At high concentrations, "in-register" associated extended beta structures are formed.

Amino Acid Sequence↗
PubMed1978

Protected homo-oligopeptide structure: Model for preferred conformation of a linear methionine heptapeptide in chloroform.

The (1)H nuclear magnetic resonance spectra for a protected linear heptapeptide of methionine, Boc-Met(7)-OMe, were measured in dimethyl-d(6) sulfoxide and C(2)HCl(3) solutions. In the former, the peptide is disordered. In C(2)HCl(3), preferred (short-range) interactions exist that dominate the overall secondary structure of the peptide. A model is proposed in which seven-membered ring structures are initiated at the NH(2)-terminus and propagate toward the carboxyl terminus. The first seven-membered ring contains a strong hydrogen bond between the amide NH of residue 2 and the carbonyl oxygen atom of the urethane blocking group. As one proceeds toward the carboxyl terminus the hydrogen bond strength of succeeding rings decreases, and at residue 5 the peptide chain assumes an extended structure that is stabilized by intermolecular hydrogen bonds. The model accounts for most of the results from (1)H NMR and infrared studies on the heptapeptide and is consistent with conformational energy calculations on homo-oligopeptides. It suggests that the COOH-terminal residues may serve as the nucleus for intermolecular peptide-peptide associations.

Journal Article↗
PubMed1978

Isolation of a peptide transport-deficient mutant of yeast.

A peptide transport mutant of a leucine-lysine auxotroph of Saccharomyces cerevisiae (strain Z1-2D) was isolated on the basis of its resistance to L-ethionyl-L-alanine. The mutant, designated Z1-2D Etar, did not utilize di- and tripeptides containing leucine or lysine although it contained peptidases which released the required amino acids from these substrates. S. cerevisiae Z1-2D Etar did not accumulate radioactivity from [14C]glycyl-L-leucine under conditions identical to those in which the parent took up the label from this dipeptide. These results indicate that the mutant lacks the cellular mechanism to transport peptides to the site of the peptidase activity and that di- and tripeptides share a common mode of entry into yeast.

Biological Transport↗
PubMed1977

Transport of [14C]Gly-Pro in a proline peptidase mutant of Salmonella typhimurium.

The transport of [14C]Gly-Pro was examined using a mutant of Salmonella typhimurium (strain TN87) deficient in an X-Pro dipeptidase and an X-Pro-Y iminopeptidase. The dipeptide was taken up by one saturable transport system having a Km of 5.3-10(-7)M and a V of 1.4 nmol/mg dry wt cell per min. The uptake of Gly-Pro was not inhibited by amino acids or tripeptides and the transport system exhibited a rather broad side chain specificity for dipeptides. Dipeptides containing hydrophobic residues were the most potent inhibitors of this dipeptide transport system exhibiting Ki values between 10(-8) and 10(-7) M. In contrast, dipeptides containing glycine residues were particularly weak inhibitors. Finally, Gly-Pro was found to be in the intact form inside the cell and was concentrated more than 1000-fold.

Amino Acids↗
PubMed1977

Peptide transport in yeast: utilization of leucine- and lysine-containing peptides by Saccharomyces cerevisiae.

A variety of leucine-containing di- and tripeptides and two lysine-containing dipeptides supported the growth of strain Z1-2D, a leucine, lysine auxotroph of Saccharomyces cerevisiae. However, (Lys)2, (Lys)3, (Lys)4, and (Lys)5 as well as Gly-Leu-Gly, three tetra- and one pentapeptide containing leucine were not utilized by the mutant. Cellular peptidases released leucine or lysine from all of these non-growth-supporting peptides, suggesting that the failure of strain Z1-2D to utilize these compounds reflects their failure to enter the yeast. Competition studies employing phenylalanine or non-leucine-containing peptides showed that the uptake of peptides into S. cerevisiae Z1-2D is distinct from that of amino acids and that di- and oligopeptides may share a common transport system. The failure of strain Z1-2D to utilize any peptide larger than (Leu)3 may indicate a transport size limit. Such a size limit would influence the construction of models that explain the action of yeast mating factors.

Biological Transport, Active↗
PubMed1976

Basis for the design of anticandidal agents from studies of peptide utilization in Canadida albicans.

The growth of Candida albicans WD 18-4, a methionine and lysine double auxotroph, on a variety of methionine- and lysine-containing peptides was determined. This yeast does not excrete extracellular peptidases. Thus, the growth response to peptides containing the required amino acid is a measure of peptide transport. A variety of methionine-containing peptides such as Met-Met, Met-Met-Met, and Met-Met-Met-Met-Met are transported. Acylation of the N-terminus of transported peptides does not affect their transport, but derivitization of the C-terminus prevents peptide uptake. In contrast, all lysine-containing peptides tested, except Lys-Gly, were not growth substrates. The inability of a peptide to substitute for the requisite amino acid was not due to the absence of cellular peptidases or to toxicity of the nonutilized peptides. Several potentially toxic amino acids were carried into Candida as a component of transported peptides. This establishes the peptide transport system as a possible tool for the design of antibiotics for Candida albicans.

Antifungal Agents↗
PubMed1975

Multiplicity of oligopeptide transport systems in Escherichia coli.

The ability of Escherichia coli K-12 4212 to utilize a variety of oligopeptides as sources of required amino acids was examined. Triornithine-resistant mutants of this strain were oligopeptide permease deficient (Opp-) as judged by their inability to utilize (Lys)3 and (Lys)4 as sources of lysine and their resistance to the toxic tripeptide (Val)3. These same mutants were able to grow when Met-Met-Met, Met-Gly-Met, Met-Gly-Gly, Gly-Met-Gly, Gly-Gly-Met, Gly-Met-Met, Met-Met-Gly, or Leu-Leu-Leu were supplied in place of the requisite amino acid. The system mediating the uptake of these peptides, herein designated Opr I, was not able to transport N-alpha-acetylated peptides, nor the tetrapeptides Met-Gly-Met-Met, Met-Met-Gly-Met, or Met-Met-Met-Gly. Competition experiments indicated that trimethionine and trileucine enter E. coli K-12 via either Opp or Opr I. Analogous results were found using the methionine, leucine-requiring auxotroph E. coli B163. It appears that more than one oligopeptide transport system exists in E. coli and that the system mediating peptide uptake is complex.

Biological Transport, Active↗
PubMed1974

Stereospecificity of tripeptide utilization in a methionine auxotroph of Escherichia coli K-12.

The stereospecificity of peptide utilization in Escherichia coli K-12 4212, a methionine auxotroph, was investigated using diastereomers of trimethionine and trimethionine methyl ester. Of the eight stereoisomers examined, only l-Met-l-Met-l-Met, l-Met-l-Met-d-Met, and d-Met-l-Met-l-Met and the corresponding methyl esters serve as growth substrates. Triornithine-resistant mutants of strain 4212 were isolated which failed to transport d-Met-l-Met-l-Met. These results provide evidence that an oligopeptide containing a d residue at its amine terminus can enter E. coli by the oligopeptide transport system.

Cell-Free System↗