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Biomedical subjects

J Horowitz

Publications and source records attributed to J Horowitz.

At least 19 recordsLinked to original sources
PubMed1992

Fluorine-19 nuclear magnetic resonance as a probe of the solution structure of mutants of 5-fluorouracil-substituted Escherichia coli valine tRNA.

In order to utilize 19F nuclear magnetic resonance (NMR) to probe the solution structure of Escherichia coli tRNAVal labeled by incorporation of 5-fluorouracil, we have assigned its 19F spectrum. We describe here assignments made by examining the spectra of a series of tRNAVal mutants with nucleotide substitutions for individual 5-fluorouracil residues. The result of base replacements on the structure and function of the tRNA are also characterized. Mutants were prepared by oligonucleotide-directed mutagenesis of a cloned tRNAVal gene, and the tRNAs transcribed in vitro by bacteriophage T7 RNA polymerase. By identifying the missing peak in the 19F NMR spectrum of each tRNA variant we were able to assign resonances from fluorouracil residues in loop and stem regions of the tRNA. As a result of the assignment of FU33, FU34 and FU29, temperature-dependent spectral shifts could be attributed to changes in anticodon loop and stem conformation. Observation of a magnesium ion-dependent splitting of the resonance assigned to FU64 suggested that the T-arm of tRNAVal can exist in two conformations in slow exchange on the NMR time scale. Replacement of most 5-fluorouracil residues in loops and stems had little effect on the structure of tRNAVal; few shifts in the 19F NMR spectrum of the mutant tRNAs were noted. However, replacing the FU29.A41 base-pair in the anticodon stem with C29.G41 induced conformational changes in the anticodon loop as well as in the P-10 loop. Effects of nucleotide substitution on aminoacylation were determined by comparing the Vmax and Km values of tRNAVal mutants with those of the wild-type tRNA. Nucleotide substitution at the 3' end of the anticodon (position 36) reduced the aminoacylation efficiency (Vmax/Km) of tRNAVal by three orders of magnitude. Base replacement at the 5' end of the anticodon (position 34) had only a small negative effect on the aminoacylation efficiency. Substitution of the FU29.A41 base-pair increased the Km value 20-fold, while Vmax remained almost unchanged. The FU4.A69 base-pair in the acceptor stem, could readily be replaced with little effect on the aminoacylation efficiency of E. coli tRNAVal, indicating that this base-pair is not an identity element of the tRNA, as suggested by others.

Acylation↗
PubMed1992

Correlations between fluorine-19 nuclear magnetic resonance chemical shift and the secondary and tertiary structure of 5-fluorouracil-substituted tRNA.

To complete assignment of the 19F nuclear magnetic resonance (NMR) spectrum of 5-fluorouracil-substituted Escherichia coli tRNA(Val), resonances from 5-fluorouracil residues involved in tertiary interactions have been identified. Because these assignments could not be made directly by the base-replacement method used to assign 5-fluorouracil residues in loop and stem regions of the tRNA, alternative assignment strategies were employed. FU54 and FU55 were identified by 19F homonuclear Overhauser experiments and were then assigned by comparison of their 19F NMR spectra with those of 5-fluorouracil-labeled yeast tRNA(Phe) mutants having FU54 replaced by adenine and FU55 replaced by cytosine. FU8 and FU12, were assigned from the 19F NMR spectrum of the tRNA(Val) mutant in which the base triple G9-C23-G12 substituted for the wild-type A9-A23-FU12. Although replacement of the conserved U8 (FU8) with A or C disrupts the tertiary structure of tRNA(Val), it has only a small effect on the catalytic turnover number of valyl-tRNA synthetase, while reducing the affinity of the tRNA for enzyme. Analysis of the 19F chemical shift assignments of all 14 resonances in the spectrum of 5-fluorouracil-substituted tRNAVal indicated a strong correlation to tRNA secondary and tertiary structure. 5-Fluorouracil residues in loop regions gave rise to peaks in the central region of the spectrum, 4.4 to 4.9 parts per million (p.p.m.) downfield from free 5-fluorouracil. However, the signal from FU59, in the T-loop of tRNA(Val), was shifted more than 1 p.p.m. downfield, to 5.9 p.p.m., presumably because of the involvement of this fluorouracil in the tertiary interactions between the T and D-loops. The 19F chemical shift moved upfield, to the 2.0 to 2.8 p.p.m. range, when fluorouracil was base-paired with adenine in helical stems. This upfield shift was less pronounced for the fluorine of the FU7.A66 base-pair, located at the base of the acceptor stem, an indication that FU7 is only partially stacked on the adjacent G49 in the continuous acceptor stem/T-stem helix. An unanticipated finding was that the 19F resonances of 5-fluorouracil residues wobble base-paired with guanine were shifted 4 to 5 p.p.m. downfield of those from fluorouracil residues paired with A. In the 19F NMR spectra of all fluorinated tRNAs studied, the farthest downfield peak corresponded to FU55, which replaced the conserved pseudouridine normally found at this position.

Acylation↗
PubMed1992

[Echinococcus cyst of the breast imitating carcinoma].

A 3 x 4 cm breast mass in a 38-year-old woman was surgically removed and was found to be an echinococcal cyst; thorough investigation failed to reveal any other hydatid cysts. Echinococcal cyst should be considered in the differential diagnosis of the much more common malignant breast mass.

Adult↗
PubMed1992

Polyarthritis associated with hydatid disease (echinococcosis) of the liver.

A 36-year-old male developed asymmetric polyarthritis during the course of hydatid disease of the liver. Excision of the hydatid cyst was accompanied by full remission of the arthritis without recurrence during the 7-year follow-up period. This sequence of clinical events suggests an eventual cause and effect relationship. A "reactive" immune mechanism, triggered by a parasite located at a distant site, appears to be responsible for this type of arthritis.

Adult↗
PubMed1992

Postsplenectomy leukocystosis: physiologic or an indicator of infection?

The records of 42 patients who underwent splenectomy following blunt abdominal trauma were reviewed to determine whether white blood cell (WBC) count is a useful indicator of acute infection in the postoperative period. Patients, ranging in age from 14 to 54 years, were divided into two groups: 1) infected (n = 18) and 2) noninfected (n = 24). Group average daily WBC counts (thousands/mm3) and differential counts (polymorphonuclear leukocyte/bands) were evaluated for the first 14 postoperative days. The infected group had a mean WBC of 21.2 and a mean differential count of 73/8. The average daily WBC count began to rise on Day 4 (WBC = 10.8) and peaked on Day 7 at 27.8. There were 30 episodes of infection: 14 pneumonias and 16 others, including sinusitis, empyema, subphrenic abscess, urinary tract infection, and bacteremias. The noninfected group had a mean WBC count of 14.2 and a mean differential of 73/5. For this group, the average WBC peaked by the postoperative Day 2 (WBC = 15.9), then the trend was downward. Thus, for patients with traumatic splenic injuries, WBC count may predict infection in the postsplenectomy period. In the noninfected group, the authors observed no average daily WBC count above 16; whereas, in the infected group, no average daily WBC count less than 16 was observed. The differential counts were not significantly different between the two groups.

Abdominal Injuries↗
PubMed1991

Fluorine-19 NMR studies of the thermal unfolding of 5-fluorouracil-substituted Escherichia coli valine transfer RNA.

19F NMR spectroscopy was used to monitor the thermal unfolding of E. coli tRNAVal labeled by incorporation of 5-fluorouracil (FUra). With rising temperatures, resonances in the 19F NMR spectrum of (FUra)tRNAVal gradually shift towards the central region of the spectrum and merge into a single broad peak above 85 degrees C. FU55 and FU12 are the first to shift, beginning at temperatures below 40 degrees C, which suggests that the initial steps of thermal denaturation of tRNAVal involve disruption of the tertiary interactions between the D- and T-arms. The acceptor stem and the FU64-G50 wobble base pair in the T-stem are particularly stable to thermal denaturation. A temperature-dependent splitting of the 19F resonance assigned to FU64, at temperatures above 40 degrees C, suggests that the T-arm of (FUra)tRNAVal exists in two conformations in slow exchange on the NMR time scale.

Base Sequence↗
PubMed1991

Recognition of Escherichia coli valine transfer RNA by its cognate synthetase: a fluorine-19 NMR study.

Interactions of 5-fluorouracil-substituted Escherichia coli tRNAVal with its cognate synthetase have been investigated by fluorine-19 nuclear magnetic resonance. Valyl-tRNA synthetase (VRS) (EC 6.1.1.9), purified to homogeneity from an overproducing strain of E. coli, differs somewhat from VRS previously isolated from E. coli K12. Its amino acid composition and N-terminal sequence agree well with results derived from the sequence of the VRS gene [Heck, J.D., & Hatfield, G.W. (1988) J. Biol. Chem. 263, 868-877]. Apparent KM and Vmax values of the purified VRS are the same for both normal and 5-fluorouracil (FUra)-substituted tRNAVal. Binding of VRS to (FUra)tRNAVal induces structural perturbations that are reflected in selective changes in the 19F NMR spectrum of the tRNA. Addition of increasing amounts of VRS results in a gradual loss of intensity at resonances corresponding to FU34, FU7, and FU67, with FU34, at the wobble position of the anticodon, being affected most. At higher VRS/tRNA ratios, a broadening and shifting of FU12 and of FU4 and/or FU8 occur. These results indicate that VRS interacts with tRNAVal along the entire inside of the L-shape molecule, from the acceptor stem to the anticodon. Valyl-tRNA synthetase also causes a splitting of resonances FU55 and FU64 in the T-loop and stem of tRNAVal, suggesting conformational changes in this part of the molecule. No 19F NMR evidence was found for formation of the Michael adduct between VRS and FU8 of 5-fluorouracil-substituted tRNAVal that has been proposed as a common intermediate in the aminoacylation reaction.

Base Sequence↗
PubMed1991

Radionuclide blood pool scintigraphy in a child with intestinal arteriovenous malformation (juvenile angiodysplasia). A case report and review of the literature.

Arteriovenous (AV) malformation or angiodysplasia of the gastrointestinal tract is a very rare cause of bleeding in children. These lesions are congenital anomalies and thought to be of hamartomatous origin. We report on a 4-year-old child with an AV malformation of the distal ileum treated by local resection. A brief review of the relevant literature is included. The importance of radionuclide blood pool scanning in the evaluation of these patients is emphasized.

Arteriovenous Malformations↗
PubMed1991

Schwannoma of the brachial plexus mimicking an apical lung tumor.

Primary tumors of the brachial plexus are unusual. We describe a patient with a large schwannoma of the lower trunk of the brachial plexus that had the radiologic appearance of an apical lung mass. Use of a posterior subscapular approach as well as intraoperative nerve action potential recording permitted resection with spared function.

Adult↗
PubMed1991

An unusual case of factitious arthritis.

Factitious arthritis is an unusual manifestation of a factitious illness. We report a case of factitious arthritis after the self insertion of needles and fragments of metallic paper clips into the knee joint area. The case illustrates an unusual presentation of Munchausen's syndrome.

Adult↗
PubMed1991

Improvement of psoriatic arthritis in a patient treated with bromocriptine for hyperprolactinemia.

We describe a woman with psoriatic arthritis who experienced a remarkable improvement of her skin and joint disease while only taking bromocriptine therapy. She was treated with bromocriptine for primary infertility due to hyperprolactinemia. The improvement in joint symptoms appeared to parallel that of the skin. More studies are required to determine the reproducibility of this observation.

Adult↗
PubMed1990

Sulphur bath and mud pack treatment for rheumatoid arthritis at the Dead Sea area.

Forty patients with classical or definite rheumatoid arthritis in a stage of active disease were treated for two weeks at a spa hotel. The patients were divided into four groups of 10. Group I was treated with daily mud packs, group II with daily hot sulphur baths, group III with a combination of mud packs and hot sulphur baths, and group IV served as a control group. The patients were assessed by a rheumatologist who was blinded to the treatment modalities. Statistically significant improvement for a period of up to three months was observed in the three treatment groups in most of the clinical indices. Improvement in the control group was minor in comparison and not statistically significant. No significant improvement was observed in any of the laboratory variables measured. Except for three mild cases of thermal reaction there were no side effects.

Arthritis, Rheumatoid↗