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Biomedical subjects

M Nichols

Publications and source records attributed to M Nichols.

At least 55 records · Page 3Linked to original sources
PubMed1989

Purification and characterization of an erythrocyte membrane protein complex carrying Duffy blood group antigenicity. Possible receptor for Plasmodium vivax and Plasmodium knowlesi malaria parasite.

A murine monoclonal antibody, named anti-Fy6, which agglutinates all human red cells except those of Fy(a-b) phenotype was used for purification and characterization of Duffy antigens. Duffy antigens are multimeric red cell membrane proteins composed of different subunits of which only one, designated pD protein, reacts in immunoblots with the murine monoclonal antibody anti-Fy6. Affinity-purified detergent-soluble antigen-antibody complex obtained from red cells, surface-labeled with 125I yielded a complex pattern of bands when separated by polyacrylamide gel electrophoresis. Proteins that react with anti-Fy6 in immunoblots are: pA and pB (greater than 100 kDa) and pD (36-46 kDa). Electroeluted pD protein aggregates and generates bands of similar molecular mass to pA and pB proteins. Electroeluted pA and pB proteins disaggregate yielding pD protein. Oligomers and monomers of pD protein are present in red cells carrying Duffy antigens and absent in Fy(a-b-) cells. Six other proteins of molecular weight ranging from 68 to 21 kDa either associate or co-purify with pD protein. These proteins are only present in Duffy antigen positive cells. The pD protein is different in Fy(a+b-) and Fy(a-b+) cells by fingerprint analysis. Human antisera identify the same proteins in red cell carrying Duffy antigens as the murine monoclonal antibody anti-Fy6.

Animals↗
PubMed1989

Cardiovascular effects of desipramine in children.

The effect of desipramine hydrochloride was studied in children who were treated for eating disorders (5), attention deficit disorder (13), or affective disturbance (3). Serial heart rate, blood pressure, ECG, and 24-hour ambulatory monitoring were recorded before treatment and at 4 and 8 weeks during treatment. Maximum dose of desipramine was 5 mg/kg/day, average 4.25. A 21% increase in heart rate and 2.5% increase in QTc at 4 weeks were sustained at 8 weeks. No dysrhythmias or clinically significant changes in blood pressure occurred. Desipramine is safe in children who have normal cardiovascular examinations and ECGs when used within the limits of the study design. The cardiovascular effects of desipramine should be kept in mind and monitored when patients are starting tricyclic antidepressant therapy such as desipramine.

Arrhythmias, Cardiac↗
PubMed1988

Yeast RNase P: catalytic activity and substrate binding are separate functions.

During tRNA biosynthesis the 5'-leader sequences in precursor tRNAs are removed by the ribonucleoprotein RNase P, an enzyme whose RNA moiety is required for activity. To clarify some aspects of the enzyme mechanism, we examined substrate binding and product formation with mutant precursor tRNAs. Mutations G-1----A or U-2----C in the Schizosaccharomyces pombe sup3-e tRNASer, which cause mispairing at or near the top of the acceptor stem, prevent the removal of the 5'-leader sequences by Saccharomyces cerevisiae RNase P. Equilibrium binding studies involving specific gel retardation of RNase P-precursor tRNA complexes showed that complexes with wild-type and A-1 and C-2 mutant precursor tRNAs had very similar dissociation constants (average Kd for sup3 = 1.5 +/- 0.2 nM). Thus, the 5'-terminal nucleotides of mature tRNA, on the 3' proximal side of the RNase P cleavage site, affect the enzyme's catalytic function but not substrate binding. The catalytic integrity of the RNA component of RNase P is not essential for binding of tRNA precursors, as demonstrated by gel retardation of micrococcal nuclease-inactivated enzyme. This suggests a possible role for the protein component of the enzyme in substrate binding. Upon restoration of base pairing to the acceptor stem in the A-1 or C-2 mutants, we found that, in addition to a requirement for pairing at these positions, conservation of the wild-type first and second nucleotides of the tRNA was necessary to obtain maximal cleavage by RNase P. This indicates a distinct sequence preference of this enzyme.

Base Sequence↗
PubMed1986

Kell blood group antigens are part of a 93,000-dalton red cell membrane protein.

Monospecific Kell blood group antibodies, of either human alloimmune or mouse monoclonal origin, react with a single surface-exposed protein of 93,000 daltons. Chymotryptic peptide maps of the 93,000-dalton protein isolated by antibodies of two different specificities (anti-K7 or anti-K14) indicate that Kell epitopes reside on the same protein. Kell protein is similar in size to band 3 protein but differs markedly in its tryptic and chymotryptic peptide maps, indicating that they are different proteins. In addition, sheep antibody to human band 3 does not react with Kell protein. Rabbit antibody to Kell protein reacts, by Western immunoblotting, with membrane proteins from Kell antigen positive red blood cells but not from those of a Ko (Kell null) cell. In intact red cells only a small portion of the Kell protein is available to lactoperoxidase-catalyzed iodination. Under nonreducing conditions Kell antigen is isolated not only as a 93,000-dalton protein but also as larger protein complexes ranging in size from above 200,000 to 115,000 daltons. Treatment of red cells with iodoacetamide, prior to isolation of Kell protein, reduces the amount of the very large complexes, but Kell protein occurs both as 115,000- and 93,000-dalton proteins.

Animals↗
PubMed1986

A single base change in the intron of a serine tRNA affects the rate of RNase P cleavage in vitro and suppressor activity in vivo in Saccharomyces cerevisiae.

Differences in the processing of dimeric tRNASer-tRNAMet precursors derived from the Schizosaccharomyces pombe sup9 wild-type and opal suppressor genes can be attributed to conformational alterations in the tRNASer anticodon/intron domain. A comparison of the patterns obtained upon transcription of the sup9+ (wild-type) and sup9-e (opal suppressor) genes in a coupled transcription/processing extract from Saccharomyces cerevisiae reveals that the latter exhibits a greatly reduced efficiency of 5'-end maturation and is susceptible to specific endonucleolytic cleavage(s) within the intron. Free energy calculations indicate that these effects coincide with a destabilization of the wild-type anticodon/intron stem and suggest that the predominant sup9-e conformer lacks secondary structure in this region. Evidence in support of this hypothesis was obtained by analyzing the processing of sup9+ and sup9-e precursors carrying the intron base substitution, G37:10, which destroys and restores, respectively, the base-pairing potential of the proposed secondary structure and comparing the strength and temperature sensitivity of sup9-e and sup9-e G37:10 suppression in vivo in S. cerevisiae. The data indicate that the anticodon/intron structure of tRNA precursors can influence the rate of RNase P cleavage in vitro and affect tRNA expression in vivo.

Base Sequence↗
PubMed1986

The nucleotide sequence, localization and transcriptional properties of a tRNALeuCUG gene from Drosophila melanogaster.

The nucleotide sequence of a tRNALeuCUG gene from Drosophila melanogaster has been determined and compared with available tRNALeuCUG sequences from other eukaryotes, as well as with the tRNALeuUUG gene of D. melanogaster. The genomic location, determined by in situ hybridization, was found to be at site 66B on chromosome 3L. This localization probably places it within one of the known, but uncharacterized, clusters of tRNA genes in this organism. In addition, the transcriptional behaviour of this tRNALeuCUG gene in various in vitro systems is described and it seems that, although the gene is transcribed in all test systems, the very A + T-rich 5'-flanking sequence of this particular gene may be somewhat inhibitory to transcription in vitro.

Animals↗
PubMed1986

Functional complementation between mutations in a yeast suppressor tRNA gene reveals potential for evolution of tRNA sequences.

Successive rounds of mutagenesis of a Schizosaccharomyces pombe strain bearing the UGA-reading sup3 tRNASer suppressor have been carried out for two cycles of inactivation and reactivation of the suppressor. The suppressor phenotype at each stage was found to involve different combinations of three mutations, A30, A53, and A67, in the sup3-UGA gene. Single mutations A30 and A53 inactivate the suppressor as does the presence of all three mutations. A67 by itself is phenotypically neutral, but in combination with either A30 or A53 suppressor function is restored. The frequency with which these and other complementation events occur in S. pombe demonstrates a significant potential for nucleotide sequence evolution in tRNA. Differential expression of the S. pombe genes in Saccharomyces cerevisiae suggests that the two yeasts have diverged at the transcriptional and RNA processing level. Processing of the mutant tRNA precursors in S. cerevisiae reveals a hierarchy of structural domains within the tRNA that vary in their importance for RNase P cleavage.

Alleles↗
PubMed1986

Anomalous origin and malposition of the pulmonary arteries (crisscross pulmonary arteries) associated with complex congenital heart disease.

Anomalous origin and malposition of the branch pulmonary arteries is an uncommon malformation that has previously been noted only at the time of pathologic examination. Two infants with complex congenital cardiac disease had malposition of the branch pulmonary arteries (crisscross pulmonary arteries) detected by angiography and confirmed during surgery and in one case, at autopsy. The presence of this clinically unsuspected lesion complicated the accurate interpretation of both the two-dimensional echocardiographic appearance of the great vessels, and the catheter course and location during cardiac catheterization. Angiography clearly defined the crisscrossing pattern of the branch pulmonary arteries. The recognition of this malformation was important in planning and executing the surgical palliation or repair for these infants.

Electrocardiography↗
PubMed1985

Dimeric tRNA gene arrangement in Schizosaccharomyces pombe allows increased expression of the downstream gene.

Three Schizosaccharomyces pombe dimeric tRNA genes, consisting of a tRNASer gene encoding a minor species with an intervening sequence followed by a tRNAMeti gene, have been described [Mao et al. (1980) Cell 21, 509-516; Hottinger et al. (1982) Mol. Gen. Genet. 188, 219-224; Willis et al. (1984) EMBO J. 3, 1573-1580]. We have examined the reason for the dimeric structure by comparing the transcriptional efficiencies and competitive abilities of the genes subcloned from the dimeric arrangement. Both of the subcloned genes are active in vivo in Saccharomyces cerevisiae, but only the tRNASer gene is efficiently transcribed in vitro. The tRNASer gene competes efficiently for transcription factors, while the tRNAMeti gene does so only weakly. Thus, it appears that the dimeric arrangement is required to support expression of the tRNAMeti gene. S. pombe genes encoding major species of tRNASer are transcribed considerably less efficiently than are the minor genes from the dimers, so coupling of the tRNAMeti gene to the minor species genes should lead to efficient production of tRNAMeti.

Cloning, Molecular↗
PubMed1984

Enhancement of the DNA breakage and cytotoxic effects of intercalating agents by treatment with sublethal doses of 1-beta-D-arabinofuranosylcytosine or hydroxyurea in L1210 cells.

4'-(9-Acridinylamino)methanesulfon-m-anisidide (m-AMSA) and other DNA intercalating agents produce protein-associated DNA strand breaks, the formation of which are mediated by topoisomerase-like chromosomal proteins. As topoisomerases would be expected to be most active during DNA replication, DNA synthesis inhibitors may alter the sensitivity of cellular DNA to intercalator-induced scission. We report that treatment of L1210 cells with 1-beta-D-arabinofuranosylcytosine (ara-C) (0.1 microM) or hydroxyurea (HU) (0.1 mM) for 18 hr resulted in a 2- to 2.4-fold enhancement of m-AMSA-induced protein-associated DNA single-strand breaks and DNA-protein cross-links as measured by alkaline elution. This enhancement was dependent on the duration of ara-C or HU treatment as well as on the concentration of ara-C or HU. Enhancement did not correlate with any alteration in cellular uptake of intercalator or with ara-C- or HU-induced alterations in the DNA synthetic rate. The DNA within nuclei isolated from ara-C- or HU-treated cells also displayed an enhanced susceptibility to m-AMSA-induced scission. There was a correlation between enhanced single-strand break formation and recruitment of cells into S-phase as well as between single-strand break formation and the production of a hypomethylated state of cellular DNA. Concurrent with the enhancement of m-AMSA-induced cellular DNA effects was a synergistic effect on m-AMSA cytotoxicity by ara-C or HU. This enhancement of intercalator effects was also found for the intercalator Adriamycin. We propose that these sublethal concentrations of ara-C and HU alter chromatin structure possibly via DNA hypomethylation and/or altered DNA-histone interactions so that intercalator-induced DNA effects are enhanced. Alternatively, the topoisomerase-like activity involved in intercalator-induced, protein-associated DNA break production may be increased in the nuclei of ara-C- or HU-treated cells.

Aminoacridines↗
PubMed1983

Increased central serotonergic activity associated with nocturnal anorexia induced by Walker 256 carcinoma.

The role of brain serotonin levels in Walker 256 tumor induced anorexia was investigated. Total and free plasma tryptophan, regional brain serotonin and 5-hydroxyindoleacetic acid were determined at night, and their relationship to nocturnal anorexia assessed by linear regression analysis. No significant difference in tryptophan, serotonin, or 5-hydroxyindoleacetic acid levels was detected between pair fed and tumor bearing rats exhibiting a 20% reduction of nighttime food intake. Tumor bearing rats with a 40% reduction in food intake had higher nighttime plasma free tryptophan and regional 5-hydroxyindoleacetic acid levels than their pair fed malnourished controls. These results indicate that increased plasma free tryptophan and elevated serotonin metabolism may not be the initial dysfunction responsible for nocturnal anorexia. However, it may contribute to the decreasing nocturnal food intake in severely anorexic tumor rats.

Animals↗
PubMed1982

Use of lymphoplasmapheresis or plasmapheresis in the management of acute renal allograft rejection.

Several recent reports have documented the value of intensive plasmapheresis as an adjunct to standard immunosuppressive therapy for patients suffering acute renal allograft rejection. We have treated four rejection episodes in three patients with intensive plasmapheresis and two rejection episodes in two additional patients with intensive lymphoplasmapheresis. Five of six rejection episodes were reversed, and four of the five patients treated have retained functioning grafts for follow-up periods ranging from 4 months to 3 years. Previous investigators have reported encouraging results using plasmapheresis, and we believe our experience supports the requirement for further controlled studies with this procedure. Moreover, we note that no previous work has been described with lymphoplasmapheresis and suggest that removal of lymphocytes, in addition to plasma, may further augment immunosuppression in the treatment of renal allograft rejection.

Acute Disease↗
PubMed1981

Protein-associated deoxyribonucleic acid strand breaks in L1210 cells treated with the deoxyribonucleic acid intercalating agents 4'-(9-acridinylamino) methanesulfon-m-anisidide and adriamycin.

The DNA intercalating agents 4'-(9-acridinyl-amino) methanesulfon-m-anisidide (m-AMSA) and adriamycin were studied by using filter elution methods to measure DNA single-strand breaks (SSB's), DNA-protein cross-links (DPC's), and double-stranded breaks (DSB's) in mouse leukemia L1210 cells. Both compounds produced SSB's and DPC's at nearly 1:1 ratios. The SSB's and DPC's were shown to be localized with respect to each other; this was inferred from the finding that filter assays based on protein adsorption completely prevented the elution of the DNA single-strand segments between SSB's. In the case of m-AMSA, which produces relatively high frequencies of DNA lesions, the possibility that a protein bridges across the SSB was excluded by alkaline sedimentation studies. Both compounds also produced DSB's, but the SSB/DSB ratios differed; the SSB/DSB ratios increase in the following order: ellipticine greater than adriamycin greater than m-AMSA greater than X-ray [results of this paper combined with those of Ross, W. E., & Bradley, M. O. (1981) Biochim. Biophys. Acta (in press)]. The o-AMSA isomer is much less cytotoxic than m-AMSA and did not produce protein-associated strand breaks. The simplest model to explain the results is that a protein becomes covalently bound to either the 3' or the 5' termini of the intercalator-induced strand breaks. At moderately cytotoxic doses, m-AMSA yielded much larger frequencies of protein-associated SSB's than did adriamycin. m-AMSA-induced protein-associated SSB's saturated at approximately 60000 per cell over a concentration range in which m-AMSA uptake by the cells was proportional to the drug concentration. m-AMSA was found to enter and exit from cells very rapidly at 37 degrees C; protein-associated SSB's and DSB's also appeared and disappeared rapidly. At reduced temperature, however, the appearance and disappearance of protein-associated SSB's could be blocked while m-AMSA entry and exit still occurred. The saturation behavior and temperature dependence suggest that the formation and disappearance of protein-associated strand breaks is enzymatic. The simplest hypothesis is that the linked protein is a nuclease, such as a topoisomerase, which becomes bound to one terminus of the strand break it produces. It is proposed that topoisomerases producing SSB's and DSB's are stimulated to different degrees by different intercalators.

Aminoacridines↗
PubMed1981

Respiratory disease in Utah coal miners.

Two hundred forty-two Utah underground coal miners volunteered to participate in a respiratory disease study. They were an older group (mean, 56 years of age) and had spent a mean of 29 years in the coal-mining industry. The prevalence of chronic bronchitis was 57%, and that of coal worker's pneumoconiosis, 25%; only one worker had progressive massive fibrosis. Significant impairment of pulmonary function was found among those with a history of cigarette smoking. Chronic bronchitis or coal worker's penumoconiosis among nonsmokers did not impair pulmonary function. There was a significant association among the nonsmokers between increasing exposure to coal dust and coal worker's pneumoconiosis, but not for changes in pulmonary function. Coal mine dust had a significant influence in causing the symptom complex of chronic cough and sputum production, and coal worker's pneumoconiosis.

Bronchitis↗
PubMed1976

Is the nexus necessary for cell-to-cell coupling of smooth muscle?

Electronmicroscopic study of electrically coupled smooth muscles was undertaken to determine the distribution of nexuses in various types of smooth muscle. The study revealed that while nexal structures were commonplace in some types of smooth muscle, they were very rare or absent in others, even though in some cases these cells were only a few nanometers distant from one another. The persistence in thin section of these structures in the main circular muscle of dog intestine after poor fixation, fixation under strain, cell shrinkage, and metabolic damage of various sorts seems to rule out the thesis that they are labile. The absence of nexuses in longitudinal muscle of dog intestine examined both by thin section and by freeze fracture suggests that in this tissue they are absent or very rare in vivo and cannot account for electrical coupling. Nexuses were discernible in thin sections of main circular muscle after a variety of experimental conditions of fixation. Metabolic inhibition or in vitro permanganate fixation partially destroyed nexal contacts. These procedures induced tissue, membrane apposition and an accompanying increase in the number of structures which resemble nexuses at low magnification (nexus-like structures). "Nexus-like" structures occurred in all smooth muscle fixed by in vitro permanganate associated with apposition of membranes and poor preservation of basement membrane. A technique of in vitro permanganate fixation was developed which prevented tissue swelling; consequently "nexus-like" structures were absent in tissues so treated. The suggestion is made that some structures described in the literature as nexuses, following permanganate fixation, may represent "nexus-like" structures. The balance of evidence suggests that nexuses need not be present for electrical coupling of some smooth muscle cells, in which other types of cell-to-cell contacts must be invoked.

Animals↗