PubMed · 14849603
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B BABUDIERI. [Aureomycin].. https://pubmed.ncbi.nlm.nih.gov/14849603/
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The interactions of calf thymus DNA with tetracycline (TC), 7-chlorotetracycline (CTC) and 6-dimethyl-7-chlorotetracycline (DMTC) were assessed employing spectrofluorometric and circular dichroism (CD) techniques. The Scatchard analysis revealed relatively lesser binding affinity of TC (Ka= 1.2 x 10(7) lmol(-1)) vis-a-vis CTC (Ka= 3.4 x 10(7) lmol(-1)) and DMTC (Ka= 3.0 x 10(7) lmol(-1)) with DNA. The data suggested both the intercalative and electrostatic nature of binding between the tetracyclines and DNA. The presence of Cu(II) augmented the interaction of tetracyclines with DNA, and resulted in red shift by 12 nm in CD spectra of tetracycline. The molar ellipticity (theta) also changed significantly for CTC and DMTC. The data unequivocally demonstrated the DNA binding potential of tetracyclines both in the presence and absence of Cu(II) ions in dark. The enhanced binding of tetracyclines in presence of Cu(II), ensuing conformational changes in DNA secondary structure to a varying extent, reflects differential reactivity of ligand chromophores.
A method using liquid chromatography-tandem mass spectrometry has been developed for determination of trace levels of tetracycline antibiotics in ground water and confined animal feeding operation waste water. Oxytetracycline (OTC), tetracycline (TC), and chlortetracycline (CTC) were extracted from water samples using both polymeric and C18 extraction cartridges. The addition of a buffer containing potassium phosphate and citric acid improved tetracycline recoveries in lagoon water. Method detection limits determined in reagent water fortified with 1 microg l(-1) OTC, TC, and CTC were 0.21, 0.20, and 0.28 microg l(-1). Method detection limits in lagoon water samples fortified at 20 microg l(-1) for OTC, TC, and CTC were 3.6, 3.1, and 3.8 microg l(-1). Variability in recovery from laboratory fortified blanks ranged from 86 to 110% during routine analysis.
We have developed a genetic system allowing for precise regulation of plasmid copy number in Escherichia coli cells. A cloning vector based on this system is described in this article. The pTC lambda 3 plasmid is a lambda replicon, but transcription controlling initiation of plasmid DNA replication starts from the PtetA promoter instead of phage lambda PR promoter. Additionally, activity of PtetA promoter is negatively controlled by the TetR repressor whose gene is located on the same plasmid vector and is induced by an analog of tetracycline, autoclaved chlortetracycline (aCT). Using different concentrations of the inducer it is possible to strictly regulate the copy number of pTC lambda 3 and thus the copy number of a cloned gene. The usefulness of the system for the regulatable production of a protein encoded by a gene inserted into pTC lambda 3 plasmid is demonstrated by dependence of beta-galactosidase activity on the lacZ gene dosage.