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Biomedical subjects

R C Thompson

Publications and source records attributed to R C Thompson.

At least 379 records · Page 21Linked to original sources
PubMed1982

Pathophysiology of Mesocestoides corti infection in the mouse.

Liver histology and serum enzyme and protein changes were studies in two strains of mice showing different initial susceptibilities to infection with Mesocestoides corti. The results show an increase in ALT and AST levels during the period of invasion and proliferation in the liver and a decrease in the levels of these two enzymes following encapsulation of the parasite in the liver and liver regeneration. A progressive loss of albumin was accompanied by increases in the levels of the beta- and gamma-globulins. These changes are discussed in the light of our knowledge of the effects of this parasite upon its host.

Alanine Transaminase↗
PubMed1982

The accuracy of protein biosynthesis is limited by its speed: high fidelity selection by ribosomes of aminoacyl-tRNA ternary complexes containing GTP[gamma S].

Guanosine 5'-[gamma-thio]triphosphate (GTP[gamma S] ) forms a stable ternary complex with polypeptide chain elongation factor Tu (EF-Tu) and aminoacyl-tRNA, and this complex binds rapidly and tightly to a properly programmed ribosome. However, the rate constant for the subsequent hydrolysis of the beta-gamma pyrophosphate bond (3.9 X 10(-3) s-1 at 5 degrees C) is less than 1/2,500th of that for the analogous reaction of GTP. We have taken advantage of this low rate to determine the rate constant for dissociation of the complex of poly(U)-programed ribosomes, EF-Tu, Phe-tRNAPhe, and GTP[gamma S] (2.7 X 10(-3) s-1) and the second-order rate constant for formation of this complex (3.3 X 10(6) M-1 s-1). Therefore, the Kd of the complex may be calculated to be 8.2 X 10(-10) M. An analogous near-cognate complex with Leu-tRNA2Leu in place of Phe-tRNAPhe has been determined by equilibrium methods to have a Kd greater than 1.7 X 10(-6) M. These results indicate that under equilibrium conditions the ribosome can distinguish cognate and near-cognate ternary complexes with great accuracy. Therefore, its failure to show this high specificity with the physiological ternary complexes containing GTP is due to the speed of GTP hydrolysis being similar to the speed of dissociation of the near-cognate complex. The low specificity of the physiological reaction is corrected by subsequent proofreading. The results reported here suggest that proofreading is necessary not simply for high accuracy but for the combination of speed and accuracy required in protein biosynthesis.

Biological Evolution↗
PubMed1982

BCG-induced inhibition and destruction of Taenia taeniaeformis in mice.

Pretreatment of mice with BCG induced a high level of protection against infection with Taenia taeniaeformis. Protection was manifested both during and after establishment by the parasite suggesting that two separate mechanisms were stimulated by BCG. The first inhibits initial establishment by the parasite and may be antibody mediated. The second is responsible for the destruction of developing strobilocerci in the liver and may require the involvement of cellular defence mechanisms.

Animals↗
PubMed1982

Entrapment neuropathy of the inferior branch of the suprascapular nerve by ganglia.

In a 37-year-old man, bilateral infraspinatus muscle weakness was associated with compression of the suprascapular nerve. The compression occurred at the spinoscapular angle by bilateral development of ganglia. The lesion was confirmed by electromyography. Surgical approaches to the area are described along with a review of the literature on different diagnosis. Complete recovery of neurologic function was documented.

Adult↗
PubMed1981

Effect of Mg2+ concentration, polyamines, streptomycin, and mutations in ribosomal proteins on the accuracy of the two-step selection of aminoacyl-tRNAs in protein biosynthesis.

Discrimination against the binding of noncognate aminoacyl (aa)-tRNAs by mRNA-programmed ribosomes is the outcome of two selection steps, one involving an aa-tRNA.EFTu.GTP complex, which occurs prior to and includes GTP hydrolysis, the other involving the aa-tRNA alone, which follows GTP hydrolysis. Conditions which lead to errors in protein synthesis have been found to influence the accuracy of one or both selection steps in a system measuring poly(U)-directed binding of Leu-tRNA2Leu. Streptomycin has a large effect only on the discrimination process following GTP hydrolysis, but the other pertubations of recognition studied, high [Mg2+], polyamines, the strA1 and ram1 mutations, affect both discrimination processes. The general result is consistent with the view that proofreading of aa-tRNA by ribosomes for the most part uses the same specificity determinants used in the initial selection of a ternary complex.

Escherichia coli↗
PubMed1981

Characterization of a hyaluronic acid-dermatan sulfate proteoglycan complex from dedifferentiated human chondrocyte cultures.

Cells grown from human articular cartilage by an explant method were shown to be dedifferentiated chondrocytes by the failure to respond to treatment with 5-bromodeoxyuridine, vitamin A, or the addition of hyaluronic acid. The major glycosaminoglycan produced by these cells was high molecular weight hyaluronic acid. The majority of the 35S-sulfated glycosaminoglycan was copolymeric chondroitin sulfate-dermatan sulfate (Mr = 2 to 2.4 X 10(4). The dermatan sulfate was present as the 4-sulfated isomer. Labeled proteoglycans were isolated from the growth media by centrifugation in either associative or dissociative cesium chloride density gradients in the presence of protease inhibitors or by precipitation with cetylpyridinium chloride and column chromatography on Sepharose CL-2B. The proteoglycans secreted into the medium by these dedifferentiated chondrocytes were large molecular weight proteoglycans (Kav = 0.23 on Sepharose CL-2B) that were able to form specific complexes with hyaluronic acid. The material isolated by the cetylpyridinium chloride precipitation was an aggregated proteoglycan (78% aggregate) that was not displaced by exogenous proteoglycan which after reduction and alkylation gave a large proteoglycan monomer (Kav = 0.23 on Sepharose CL-2B). These findings are in direct contrast to the report of small molecular proteoglycans isolated from cultures of dedifferentiated chrondrocytes obtained from other species.

Bromodeoxyuridine↗
PubMed1981

A GTPase reaction accompanying the rejection of Leu-tRNA2 by UUU-programmed ribosomes. Proofreading of the codon-anticodon interaction by ribosomes.

The characteristics of a GTPase reaction between poly(U)-programmed ribosomes, EFTu . GTP, and the near-cognate aminoacyl (aa)-tRNA, Leu-tRNA Leu 2, have been studied to assess the role of this reaction in proofreading of the codon-anticodon interaction. The reaction resembles the GTPase reaction with cognate aa-tRNAs and EFTu . GTP in its substrate requirements, in its involving EFTu . GTP . aa-tRNA ternary complexes, and in its requiring a free ribosomal A-site. The noncognate reaction differs from the cognate one in that aa-tRNA becomes stably bound to the ribosomes only 5% of the time; it therefore seems best characterized as an abortive enzymatic binding reaction. The rate of reaction is a significant fraction (4%) of that of the cognate aa-tRNA, indicating that recognition of ternary complexes by ribosomes involves a level of error greater than that of translation as a whole. The rejection of the noncognate aa-tRNA following GTP hydrolysis is therefore a vital step in the translation process and fulfills the criteria set for a proofreading reaction. Leu-tRNA Leu 2 which escapes rejection through proofreading, forms a stable complex with the ribosomal A-site, so it appears that the Leu-tRNA2 which was rejected never reached the A-site and that proofreading precedes full A-site binding.

Anticodon↗
PubMed1981

Measurement of pseudoephedrine hydrochloride dissolution using chloride-ion electrode.

Experiments were performed to determine the suitability of using a chloride-ion electrode for the measurement of pseudoephedrine hydrochloride dissolution from commercially available compressed tablets. Dissolution experiments were carried out in 500 ml of distilled water using the USP paddle method at 100 rpm. Both chloride ion and pseudoephedrine (UV spectrophotometry) were measured at six different sampling times. Percent dissolved versus time values were linearized on a log-normal probability basis. The slopes of individual lines obtained from the chloride and pseudoephedrine measurements were compared using a Student t test and did not differ significantly (t = 0.415, df = 5, p greater than 0.05). In addition to providing an efficient, inexpensive, and simple method for measuring pseudoephedrine hydrochloride dissolution rates, the chloride-ion electrode could be used in the measurement of dissolution rates for a wide variety of drugs available as hydrochloride salts.

Chlorides↗
PubMed1980

Single turnover kinetic studies of guanosine triphosphate hydrolysis and peptide formation in the elongation factor Tu-dependent binding of aminoacyl-tRNA to Escherichia coli ribosomes.

The rates of GTP hydrolysis and peptide formation during the reaction of Phe-tRNA . elongation factor Tu . GTP complex with acetyl-Phe-tRNA polyuridylate-programmed ribosomes have been measured. The GTPase reaction is second-order up to reactant concentrations of 0.2 microM and has a rate constant of 5 X 10(6) M-1 s-1 at 5 degrees C and 5 mM Mg2+, pH 7.2. The formation of peptide shows a lag phase and has a rate constant of 0.4 S-1 under these conditions. The results of a series of experiments between 5 degrees C and 25 degrees C show that GTP hydrolysis and peptide formation have Arrhenius activation energies of 13.1 and 15.3 kcal mol-1, respectively. The results indicate that these reactions proceed in vitro at rates comparable to those observed for protein biosynthesis in vivo, and that peptide bond formation occurs after GTP hydrolysis.

Bacterial Proteins↗