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Biomedical subjects

I Schwartz

Publications and source records attributed to I Schwartz.

At least 127 records · Page 7Linked to original sources
PubMed1982

Molecular cloning and regulation of expression of the genes for initiation factor 3 and two aminoacyl-tRNA synthetases.

A 22-kilobase fragment of the Escherichia coli chromosome which contains the genes for translation initiation factor 3, phenylalanyl-tRNA synthetase, and threonyl-tRNA synthetase was cloned into plasmid pACYC184. The hybrid plasmid (designated pID1) complements a temperature-sensitive pheS lesion in E. coli NP37. pID1-transformed NP37 overproduce initiation factor 3 and phenylalanyl-tRNA synthetase. Gene expression from pID1 was studied in vitro in a coupled transcription-translation system and in minicells. The results suggest that the genes for initiation factor 3 and phenylalanyl- and threonyl-tRNA synthetase are regulated by different mechanisms.

Amino Acyl-tRNA Synthetases↗
PubMed1981

Physiological and anatomical characteristics of primary vestibular afferent neurons in the bullfrog.

Intracellular recordings were made in the VIIIth nerve of the bullfrog (Rana catesbiana) to measure the membrane characteristics and obtain records of spontaneous and evoked spike activity of primary semicircular canal afferents. Physiological stimulation of the canals was achieved by rotating the preparation on a servomotor driven turntable with the animals' head centered in the rotational axis. The responses of each neuron to sinusoidal rotations at frequencies of 0.05Hz, 0.5Hz and for impulsive accelerations of 400 deg/sec2 were obtained. Membrane characteristics measured included the cell resting and action potential amplitude, and spike-activation threshold for applied currents. Physiologically characterized neurons were injected with horseradish peroxidase by applying pneumatic pressure and/or iontophoretic currents to the micropipettes containing 5% HRP in 1 M KCI. Following survival times of 12--48 h, the VIIIth nerve and attached vestibular end organ was removed for histochemical processing using a diaminobenzidine procedure to visualize the HRP reaction product. Light microscopy was used to discern the anatomical features of the neurons and to trace their peripheral dendritic trajectories from the ganglion to their termination(s) in the crista. Our studies have revealed that the bullfrog's primary vestibular afferents are characterized by a broad range of soma and axon diameters which correspond to an equally broad range of spontaneous and evoked activity characteristics. The largest neurons had more irregular spontaneous firing rates and consistently exhibited the greatest gain and smallest phase shifts with respect to head acceleration. These neurons consistently terminated at or near the central region of the crista. On the other hand, the smallest neurons were characterized by having the most regular spontaneous discharge patterns, the lowest gains, and greatest phase shifts with respect to head acceleration. Our findings are thus consistent with the view that the anatomical features of the primary vestibular neurons are important in determining the neuron's physiological characteristics. In terms of response dynamics our observations indicate that the receptors in the frog's crista ampullaris are heterogeneous and differentially sensitive to a wide range of stimulus frequencies.

Afferent Pathways↗
PubMed1980

Photochemical cross-linking of initiation factor-3 to Escherichia coli 30 S ribosomal subunits.

Initiation factor-3 has been photochemically cross-linked to Escherichia coli 30 S ribosomal subunits by means of near-ultraviolet (> 285 nm) irradiation. The cross-linking was judged to be specific since noncovalent binding was required for subsequent cross-linking and was prevented by the presence of 0.5 M NH4Cl or 0.5 mM aurintricarboxylic acid. Covalent attachment reached its maximum level of 8.5 to 11% of the noncovalently bound IF-3 after 60 min of irradation. Cross-linking was unaffected by the presence of the photosensitizer, acetone (5 or 10%), but was reduced to 30 to 40% of its maximum level by addition of 5 mM dithiothreitol, a free radical scavenger. Analysis of the 14C-labeled IF-3 x 30 S subunit covalent complex revealed that the IF-3 was distributed between the protein and RNA of the subunits in a 3:1 ratio. The target proteins have been identified as S7, S11, S12, S18, and S21 by immunochemical techniques.

Acetone↗
PubMed1980

Aortic grafting procedures: tailoring the options.

Records from 165 patients who had received aortoiliac or aortofemoral bypass grafts were reviewed. The overall five-year patency rate was 88%. There was no significant difference in operative duration, amount of blood transfused, postoperative complications, and life table patency rates when comparisons were made of unilateral and bilateral grafts, of patients who underwent sympathectomy and those who did not, or of aortofemoral and aortoiliac grafts. When bypass grafting included an additional procedure, the amount of blood transfused and the number of postoperative complications increased significantly. We conclude that (1) the decision to operate should be based on symptoms, (2) the site of anastomosis should be chosen from anatomic characteristics, and (3) other procedures should not be performed except to achieve obvious therapeutic goals and to assure graft patency.

Aorta, Abdominal↗
PubMed1979

Covalent cross-linking of transfer ribonucleic acid to the ribosomal P site. Mechanism and site of reaction in transfer ribonucleic acid.

The covalent cross-linking of unmodified Escherichia coli N-acetylvalyl-tRNA to the 16S RNA of Escherichia coli ribosomes upon near-UV irradiation previously reported by us [Schwartz, I., & Ofengand, J. (1978) Biochemistry 17, 2524--2530] has been studied further. Up to 70% of the unmodified tRNA, nonenzymatically bound to tight-couple ribosomes at 7 mM Mg2+, could be cross-linked by 310--335-nm light. Covalent attachment was solely to the 16S RNA. It was dependent upon both irradiation and the presence of mRNA but was unaffected by the presence or absence of 4-thiouridine in the tRNA. The kinetics of cross-linking showed single-hit behavior. Twofold more cross-linking was obtained w-th tight-couple ribosomes than with salt-washed particles. Puromycin treatment after irradiation released the bound N-acetyl[3H]valine, demonstrating that the tRNA was covalently bound at the P site and that irradiation and covalent linking did not affect the peptidyl transferase reaction. Cross-linking was unaffected by the presence of O2, argon, ascorbate (1 mM), or mercaptoethanol (10 mM). Prephotolysis of a mixture of tRNA and ribosomes in the absence of puly(U2,G) did not block subsequent cross-linking in its presence nor did it generate any long-lived chemically reactive species. There was a strong tRNA specificity. E. coli tRNA1Val and tRNA1Ser and Bacillus subtilis tRNAVal and tRNAThr could be cross-linked, but E. coli tRNA2Val, 5-fluorouracil-substituted tRNA1Val, tRNAPhe, or tRNAFMet could not. By sequence comparison of the reactive and nonreactive tRNAs, the site of attachment in the tRNA was deduced to be the 5'-anticodon base, cmo5U, or ,o5U in all of the reactive tRNAs. The attachment site in 16S RNA is described in the accompanying paper [Zimmerman, R. A., Gates, S. M., Schwartz, I., & Ofengand, J. (1979) Biochemistry (following paper in this issue)]. The link between tRNA and 16S RNA is either direct or involves mRNA bases at most two nucleotides apart since use of the trinucleotide GpUpU in place of poly(U2,G) to direct the binding and cross-linking of N-acetylvalyl-tRNA to the P site did not affect either the rate or yield of cross-linking. Both B. subtilis tRNAVal (mo5U) and E. coli tRNA1Val (cmo5U) gave the same rate and yield of cross-linking when directed by the trinucleotide GpUpU. Therefore, the presence of the charged carboxyl group in the cmo5U-containing tRNA apparently does not markedly perturb the orientation of this base with respect to its reaction partner in the 16S RNA. The cross-linking of AcVal-tRNA only takes place from the P site. At 75 mM KCl and 75 mM NH4Cl, less than 0.4% cross-linking was found at the A site, while 55.5% was obtained at the P site. However, when the salt concentration was lowered to 50 mM NH4Cl, 5% cross-linking to the A site was detected, compared to 49% at the P site. Thus, a simple change in the ionic strength of the incubation mixture was able to alter the affinity labeling pattern of the ribosome.

Ascorbic Acid↗
PubMed1978

Photochemical cross-linking of unmodified acetylvalyl-tRNA to 16S RNA at the ribosomal P site.

Acetylvalyl-, acetylphenylalanyl-, and formylmethionyl-tRNA which were derivatized at their 4-thiouridine residues with the photoaffinity label, p-azidophenacyl bromide, were nonenzymatically bound to salt-washed ribosomes. More than 90% of the binding was to the P site as judged by reactivity with puromycin. Subsequent irradiation (greater than 310 nm) of the tRNA-ribosome complexes resulted in the covalent linking of only the acetylvalyl-tRNA to the 30S subunit. Attachment was solely to the 16S RNA with an efficiency of cross-linking of 13--15%. Covalent linking was 90% inhibited by prior treatment with puromycin, showing that the covalent linking reaction had taken place at the P site. Cross-linking required irradiation and mRNA but was not dependent on the presence of the photoaffinity probe in the tRNA. tRNAs whose 4-thiouridine had been modified with unreactive analogues of p-azidophenacyl bromide or unmodified acetylvalyl-tRNA exhibited the same cross-linking behavior as photoaffinity probe-modified acetylvalyl-tRNA. Furthermore, even acetylvalyl-tRNA whose 4-thiouridine had been removed by treatment with H2O2 was quantitatively as active as unmodified tRNA. These results provide the first demonstration of direct photochemical cross-linking of tRNA to ribosomes.

Affinity Labels↗
PubMed1978

The effect of phenobarbital on the metabolism of meperidine in normal volunteers.

Phenobarbital has been observed clinically to alter the metabolism of meperidine, with resultant enhanced toxicity. In order to determine if this effect occurs consistently, 12 health volunteers were entered into a two-way, crossover study comparing the pharmacokinetics and metabolism of meperidine after pretreatment with both phenobarbital and placebo. Phenobarbital pretreatment had no significant effect on serum levels or the half-life of meperidine. However, phenobarbital pretreatment resulted in a decrease in the cumulative excretion of meperidine and an increase in the cumulative excretion of the N-demethylated metabolite normeperidine. Similarly, phenobarbital pretreatment resulted in a decrease in meperidinic acid and increase in normeperidinic acid. In addition, phenobarbital pretreatment also significantly altered the hepatic clearance of meperidine, indicating an increase in the hepatic N-demethylation of meperidine. Since normeperidine has been reported to be less efficacious and more toxic than meperidine, this reported interaction may be important clinically, especially with repeated doses.

Adult↗
PubMed1977

A potentially toxic drug interaction between pethidine (meperidine) and phenobarbitone.

The concomitant administration of pethidine (meperidine) and phenobarbitone results in enhanced sedation in a patient previously tolerant of pethidine. A complete analysis of pethidine kinetics and metabolism was performed in this patient, in four additional patients undergoing similar treatment but not receiving phenobarbitone, and in a volunteer after placebo and phentobarbitone pretreatment. The results indicate that phentobarbitone enhances the production of the toxic metabolite norpethidine by increasing N-demethylation.

Adult↗
PubMed1975

Management of the acute abdomen in children with leukemia.

With the increase in remission and survival in children with acute leukemia, the complication of acute abdomen has become increasingly important in the total care of these children. A total of 286 children with acute leukemia was treated at Memorial Hospital between 1966 and 1971. Sixteen or 5.6% of these children developed an acute abdomen during the course of their disease. During the same period, many other children developed symptoms and signs mimicking an acute abdomen. Of the 9 children treated surgically, 5 were long-term survivors. Two children treated conservatively died, and 5 patients were diagnosed at autopsy. Prognosis was better in those patients in remission at the time of surgery, and where remission was maintained by immediately restarting antileukemic chemotherapy. A more aggressive surgical approach to the acute abdomen, combined with careful supportive measures, is further adding to the numbers of long-term survivors in childhood leukemia.

Abdomen, Acute↗
PubMed1975

Photoaffinity labeling of the ribosomal A site with S-(p-azidophenacyl)valyl-tRNA.

S-(p-Azidophenacyl)valyl-tRNA, an analog of valyl-tRNA which has a photoaffinity label attached to its 4-thiouridine residue, was bound to the ribosomal A site at 10 mM Mg2+. Binding was stimulated 25-fold by the presence of elongation factor EFTu. Photoactivation of the p-azidophenacyl group by irradiation resulted in covalent linking of 6% of the noncovalently bound tRNA to the ribosomes. Covalent linking was dependent on the simultaneous presence of ribosomes, poly(U2,G),EFTu.GTP, required irradiation, and did not occur when S-(phenacyl)valyl-tRNA, a nonphotolyzable analog, replaced S-(p-azidophenacyl)valyl-tRNA. The attached tRNA was distributed approximately equally between both the 30S and 50S subunits. At the 30S subunit, 30% of the tRNA was bound to protein while 70% was linked to 16S RNA. At the 50S subunit, however, negligible binding to the 23S RNA was observed. More than 90% of the tRNA was attached to low molecular weight material according to sodium dodecyl sulfate-sucrose gradient analysis, and more than 87% of this fraction consisted of tRNA-protein complexes as assayed by phenol solubility and electrophoretic mobility before and after protease treatment. These results, in conjunction with our previous report (I. Schwartz and J Ofengand (1974), Proc. Natl. Acad. Sci. U.S.A. 71, 3951) which showed that covalent linking of this same tRNA derivative at the ribosomal P site resulted in attachment solely to the 16S RNA, demonstrate that 16S, but not 23S or 5S rRNA, is an important component of the tRNA binding site in the region of the 4-thiouridine residue and furthermore show that ribosomal A and P sites are topologically distinct.

Affinity Labels↗