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H Sternbach

Publications and source records attributed to H Sternbach.

85 records · Page 5Linked to original sources
PubMed1970

Micro-analysis of pure deoxyribonucleic acid-dependent ribonucleic acid polymerase from Escherichia coli. Action of heparin and rifampicin on structure and function.

By using micro disc electrophoresis and micro-diffusion techniques, the interaction of pure DNA-dependent RNA polymerase (EC 2.7.7.6) from Escherichia coli with the template, the substrates and the inhibitors heparin and rifampicin was investigated. The following findings were obtained: (1) heparin converts the 24S and 18S particles of the polymerase into the 13S form; (2) heparin inhibits RNA synthesis by dissociating the enzyme-template complex; (3) rifampicin does not affect the attachment of heparin to the enzyme; (4) the substrates ATP and UTP are bound by enzyme loaded with rifampicin; (5) rifampicin is bound by an enzyme-template complex to the same extent as by an RNA-synthesizing enzyme-template complex. From this it is concluded that the mechanism of the inhibition of RNA synthesis by rifampicin is radically different from that by heparin. As a working hypothesis to explain the inhibitory mechanism of rifampicin, it is assumed that it becomes very firmly attached to a position close to the synthesizing site and only blocks this when no synthesis is in progress.

Adenosine Triphosphatases↗
PubMedDate not supplied

Aminoacylation of tRNAs as critical step of protein biosynthesis.

Isoleucyl-tRNA synthetases isolated from commercial baker's yeast and E coli were investigated for their sequences of substrate additions and product releases. The results show that aminoacylation of tRNA is catalyzed by these enzymes in different pathways, eg isoleucyl-tRNA synthetase from yeast can act with four different catalytic cycles. Amino acid specificities are gained by a four-step recognition process consisting of two initial binding and two proofreading steps. Isoleucyl-tRNA synthetase from yeast rejects noncognate amino acids with discrimination factors of D = 300-38000, isoleucyl-tRNA synthetase from E coli with factors of D = 600-68000. Differences in Gibbs free energies of binding between cognate and noncognate amino acids are related to different hydrophobic interaction energies and assumed conformational changes of the enzyme. A simple hypothetical model of the isoleucine binding site is postulated. Comparison of gene sequences of isoleucyl-tRNA synthetase from yeast and E coli exhibits only 27% homology. Both genes show the 'HIGH'- and 'KMSKS'-regions assigned to binding of ATP and tRNA. Deletion of 250 carboxyterminal amino acids from the yeast enzyme results in a fragment which is still active in the pyrophosphate exchange reaction but does not catalyze the aminoacylation reaction. The enzyme is unable to catalyze the latter reaction if more than 10 carboxyterminal residues are deleted.

Escherichia coli↗
PubMedDate not supplied

Stimulation of transcription of the yeast tRNATyr gene in cell-free extracts by tyrosyl-tRNA synthetase.

Eukaryotic transfer RNA genes have two internal discontinuous control regions, the A and B blocks, which correspond approximately to the D-stem and the pseudo-U arm of tRNA. In reconstituted transcription systems at least two components are required to direct accurate initiation by RNA polymerase (refs 4,5). However, little is known about the mechanism of interaction of the internal promoter sequences with factors and RNA polymerase C within the transcription complex, although tRNA-like conformation of the B block sequence was surmised to be critical for DNA recognition. By analogy with the 5S RNA system, where a transcription factor required for 5S DNA expression was shown to interact both with 5S RNA and with the noncoding strand of the 5S gene, we explored the possibility that a protein which normally binds to tRNA could also interact with the tRNA gene and regulate its transcription. Here we show that in vitro transcription of the yeast SUP4 tRNATyr gene in crude yeast extracts is strongly stimulated by tyrosyl-tRNA synthetase (TyrRS) but not by two other non-cognate synthetases. Substrates of the synthetase, tRNATyr and tyrosine, interfere with stimulation of tRNA synthesis.

Amino Acyl-tRNA Synthetases↗
PubMedDate not supplied

Antibiotics: neuropsychiatric effects and psychotropic interactions.

Antibiotics are the second most commonly prescribed class of medication in the United States. An awareness and understanding of their potential effects on the central nervous system and their interactions with psychotropic agents is important in the evaluation of neuropsychiatric signs and symptoms in patients. Since the introduction of antibiotic agents in the 1930s, numerous (primarily anecdotal) reports have appeared describing psychiatric side effects ranging from anxiety and panic to major depression, psychosis, and delirium in patients with and without a premorbid psychiatric history. Risk factors have included prior psychopathology, coexisting medical conditions, slow acetylator status, advanced age, concomitant medications, and increased permeability of the blood-brain barrier, as well as high antibiotic dosage and intrathecal or intravenous administration. Psychiatric toxicity may result from various mechanisms of action, including antagonism of gamma-aminobutyric acid or pyridoxine, adverse interactions with alcohol, or inhibition of protein synthesis. Adverse pharmacokinetic and pharmacodynamic interactions between antibiotics and concomitant medications including lithium, benzodiazepines, carbamazepine, valproate, neuroleptics, antidepressants, methadone, and disulfiram have also been reported. Because such effects are often not recognized by clinicians, accurate epidemiologic data on their incidence are not available.

Anti-Bacterial Agents↗