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J C Tabet

Publications and source records attributed to J C Tabet.

9 recordsLinked to original sources
PubMed1992

Surface-induced dissociation of protonated peptides: implications of initial kinetic energy spread.

Surface-induced dissociation (SID) has been used to produce daughter ion spectra of small protonated peptides generated by fast atom bombardment (FAB). The relative abundances of daughter ions depends critically upon the energy of the ion/surface collision. A wide array of decomposition processes may be observed using ELAB collision energies in the range 10-20 eV. At approximately 13-eV collision energy, the variety of decomposition processes is maximized for the small peptides studied; hence, maximum structural information may be deduced. Collisionally-activated dissociations (CAD) using argon gas and the identical protonated peptides could not produce as large an array of daughter ions in a constant condition experiment. An apparent contradiction is thereby posed because SID is known to produce a narrow distribution of ion internal energies relative to CAD. This apparent contradiction is resolved by considering the rather large kinetic energy spread of ions leaving the FAB source. For the SID process, this large initial kinetic energy distribution is converted into a significantly wider spread in center-of-mass collision energy, leading to a broader variety of decomposition processes (high and low energy) compared to CAD.

Amino Acid Sequence↗
PubMed1992

Influence of methoxy and nitro groups in the oxidative metabolism of naphtho[2,1-b]furan.

In the present study, we have investigated the role of methoxy and nitro groups in the oxidative metabolism of naphtho[2,1-b]furan. Hepatic microsomes were used to investigate the aerobic metabolism of naphtho[2,1-b]furan (compound A), 2-nitro-naphtho[2,1-b]furan (compound B) and 7-methoxy-naphtho [2,1-b]furan (compound C) and comparison of the metabolites formed was made using HPCL analysis and NMR, mass and UV-visible spectrometry. The different metabolic pathways investigated were compared with the previously reported metabolism of 7-methoxy-2-nitro-naphtho[2,1-b]furan (compound D). Naphtho[2,1-b]furan yield metabolites of both the furan and benzene rings, while metabolites formed from 7-methoxy-naphtho[2,1-b]furan and 2-nitro-naphtho [2,1-b]furan were derived entirely as a result of enzymic attack on the first benzene ring.

Animals↗
PubMed1991

Vitamin K dependent carboxylation: determination of the stereochemical course using 4-fluoroglutamyl-containing substrate.

The stereochemical course of the vitamin K dependent carboxylation has been elucidated using a (4S)-4-fluoroglutamyl-containing pentapeptide as a substrate. The absolute configuration of the [13C]-4-carboxy-4-fluoroglutamate obtained when the carboxylation was carried out with 13C-labeled sodium bicarbonate, was determined after reduction of the [13C]-4-carboxy-4-fluoroglutamyl residue into 4-fluoro-5,5'-dihydroxyleucine, hydrolysis, lactonization, and peracetylation. The absolute configuration at C-4 was determined to be S by locating the 13C label in the lactone ring of the trans isomeric lactone and in the hydroxymethyl group of the cis isomer following HPLC separation of both isomers and analysis by GC/MS/MS techniques. It follows that the vitamin K dependent carboxylation occurs with inversion of configuration.

Amino Acid Sequence↗
PubMed1990

Management of inverted papilloma.

This paper updates a 1981 report on the management of inverted papilloma. In that report, routine lateral rhinotomy with en bloc resection of the lateral nasal wall, including the entire schneiderian membrane, was recommended. This report emphasizes the use of computed tomography scanning in management planning. Of 33 patients with inverted papilloma treated between 1969 and 1987, 7 had associated squamous cell carcinoma. Twenty-two patients with IP alone were treated with medial maxillectomy; however, 3 patients have been successfully treated with either a Caldwell-Luc/ethmoidectomy or an external ethmoidectomy for localized disease. The use of computed tomography capable of higher resolution allowed preoperative determination of the extent of disease, enabling the surgeon to plan the surgery more precisely. Patients were followed for an average of 9.6 years. Recurrent disease occurred in one patient (4%) following a lateral rhinotomy/medial maxillectomy approach. The principles set forth in this series of patients remain the same as those previously described due to the unique characteristics of this tumor: its ability to destroy bone, its tendency to recur, and its association with malignancy. The technique of lateral rhinotomy and en bloc excision of the lateral nasal wall, followed by meticulous removal of all mucosa in the ipsilateral paranasal sinuses, remains the standard therapy.

Adult↗
PubMed1990

Wound infection in head and neck surgery: prophylaxis, etiology and management.

Antibiotic prophylaxis in clean-contaminated major head and neck surgery is mandatory. Many prospective, randomized and double blind studies have established the efficacy of antibiotics against a large spectrum of bacteria. Prophylaxis should be initiated prior to surgery, and prolonged administration of antibiotics beyond the first 24 hours following surgery is unnecessary. The experience of the Eye and Ear Hospital of Pittsburgh is presented along with other studies concerning the effect of different regimens on wound outcome. The pathophysiology, bacteriology, evaluation and treatment of a postoperative infection are discussed, emphasizing the importance of gentle tissue handling and meticulous surgical technique.

Anti-Bacterial Agents↗
PubMed1988

Identification of dekamycin antibiotics.

Dekamycin was isolated from strain DK5 of Streptomyces fradiae, and purified by ion-exchange column chromatography. Excellent separation of N-acetylated derivatives of the antibiotic mixture was achieved by two different methods, flash chromatography and high-performance liquid chromatography. Mass spectrometry (252Cf plasma desorption mass spectrometry, fast atom bombardment) for the analysis of N-acetyldekamycins (neomycin B, neomycin C, neamine and ribostamycin) was mainly used to confirm the molecular weight of a structure deduced by 1H and 13C NMR analyses.

Acetylation↗
PubMed1985

Abierixin, a new polyether antibiotic. Production, structural determination and biological activities.

A new polyether antibiotic, abierixin, was found in the mycelium of a culture broth of nigericin-producing Streptomyces albus NRRL B-1865. Abierixin was extracted with organic solvents and purified by column chromatography and HPLC. The structure of abierixin was determined by FAB/MS/MS and CI/MS/MS and 1H and 13C NMR spectrometries. Abierixin exhibited weak antimicrobial and ionophorous activities, low toxicity but good anticoccidial activity. Nigericin biosynthesis from abierixin is discussed.

Animals↗
PubMed1976

Degradation of [14C]photodieldrin by Trichoderma viride as affected by other insecticides.

Various soil fungi were tested for their capacity to degrade the insecticide [14C]photodieldrin. Of nine species investigated, Trichoderma viride was the only one which degraded the insecticide to an appreciable extent into water-soluble, non-insecticidal compounds within 4-5 weeks. These products amounted to 32-41% of the radiocarbon applied to the culture media. The degradation was a function of live mycelia, which metabolized the insecticide and excreted water-soluble compounds into the culture media. Since soils usually contain a mixture of pesticide residues, the effects of several chlorinated hydrocarbon insecticides on the capacity of the fungus to degrade [14C]photodieldrin were studied. Thus, in fungal cultures treated with compounds structurally similar to photodieldrin, such as aldrin and dieldrin, only 4-17% of the applied radiocarbon was water-soluble and more photodieldrin remained. In controls, however, 35% of the applied radiocarbon was in the form of water-soluble products and less photodieldrin remained. The degradation of [14C]photodieldrin by T. viride, with time, was associated with a continuous decline of hexane-soluble radiocarbon and a steady increase of water-soluble metabolites, which appeared in the fungal media. The amount of hexane-soluble radiocarbon in mycelia was directly related to the fungal mass.

Biodegradation, Environmental↗