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Biomedical subjects

J McMahon

Publications and source records attributed to J McMahon.

At least 91 records · Page 5Linked to original sources
PubMed1986

Analysis of the autophosphorylation activity of transformation defective mutants of avian erythroblastosis virus.

The v-erb B protein of avian erythroblastosis virus (AEV) possesses an associated protein kinase activity in vitro. Analysis of temperature-sensitive mutants, and nonconditional host range mutants of AEV demonstrated that there was no simple correlation between this autophosphorylation activity and the transformation ability of the various AEV mutants. These data suggest that although this kinase activity may be central to transformation by AEV it is in itself insufficient.

Alpharetrovirus↗
PubMed1986

Determination of IgM and IgG antibodies to Toxoplasma using the IFA test, ELISA, and Dot-ELISA procedures.

The dot enzyme-linked immunosorbent assay (Dot-ELISA) and the enzyme-linked immunosorbent assay (ELISA) were compared with the immunofluorescent antibody test (IFA) for detection of IgM- and IgG-specific antibodies to human toxoplasmosis. Reciprocal titers were determined in all three assays using sera from 56 patients with suspected toxoplasmosis or with symptoms and diseases requiring exclusion of toxoplasmosis and control sera from 56 healthy persons. Using the Dot-ELISA, six patient sera (10.7%) were positive at titers of greater than equal to 1024 for IgM antibodies (titer range 1024-16 384) and 47 sera (84%) were positive for IgG antibodies (titer range 16-262 144) at a titer of greater than or equal to 16. One control serum was reactive for IgM (titer 1024) and 10 control sera (18%) were positive for IgG in the Dot-ELISA. In the ELISA, at titers of greater than or equal to 128, five sera (9%) were reactive for IgM (titer range 128-512) and 52 sera (92.8%) were reactive for IgG (titer range 32-8192) at a titer of greater than or equal to 32; no control sera gave positive reactions for IgM while 10 sera (18%) were positive for IgG in the ELISA. Using the IFA test at reciprocal titers of greater than or equal to 16, four sera (7.1%) were positive for IgM (titer range 32-512), and 51 sera (91%) were positive for IgG (titer range 16-8192). None was reactive for IgM, and eight sera (14%) were positive for IgG (titer range 32-128) in the IFA test. The Dot-ELISA correlated well with the IFA test (correlation coefficient = 0.895) and the ELISA correlated slightly higher with the IFA test (correlation coefficient = 0.910) for detection of IgG antibodies to Toxoplasma gondii.

Enzyme-Linked Immunosorbent Assay↗
PubMed1986

Activation of a cryptic TACTAAC box in the Saccharomyces cerevisiae actin intron.

We constructed a translational fusion between the Saccharomyces cerevisiae actin gene and the Escherichia coli beta-galactosidase structural gene such that expression of beta-galactosidase activity required accurate splicing of the actin intron. Using this chimeric gene, we generated a series of internal deletions which removed the TACTAAC box or, in addition, TACTAAC-like sequences within the intron. Analysis of the fusion transcripts produced in these deletions allowed us to conclude that the TACTAAC-like sequence TACTAAG can substitute, albeit inefficiently, for the authentic TACTAAC box in the splicing process. These results indicate that the yeast splicing machinery can utilize a cryptic TACTAAC box, but there are requirements for primary sequence and proper position.

Actins↗
PubMed1985

An investigation of the structural changes occurring in a cetostearyl alcohol/cetrimide/water gel after prolonged low temperature (4 degrees C) storage.

Structural changes in a ternary gel prepared using the mixed emulsifier system of cetrimide and cetostearyl alcohol after prolonged low temperature (4 degrees C) storage have been studied using freeze-etch transmission electron microscopy and other techniques. The system changed from an opaque smooth gel of high viscosity, low conductivity and low free water, to a pearlescent milky lotion of low viscosity, high conductivity and high free water. Subsequent equilibration of the thinned system to room temperature (25 degrees C) over 48 h produced an opaque granular gel of similar consistency, but slightly higher conductivity and higher free water than the initial sample. Microscopical examination by both differential interference contrast and freeze-etch electron microscopy showed the system changed from one consisting of a liquid crystalline network localized around cetostearyl alcohol particles, to a system consisting of large waxy plates coexisting with some residual liquid crystalline network. A supportive mechanism for the thinning of the ternary gel at prolonged low temperature storage has been inferred by comparing data with that produced by other workers studying the fusion of phospholipid membranes considered to be morphologically similar to the liquid crystalline network observed in this ternary gel.

Cetrimonium↗
PubMed1983

Comparison of scores obtained on the PPVT and the PPVT-R.

The purpose of this study was to compare age equivalent values obtained from the PPVT and PPVT-R. The 80 subjects, ages 3:6 to 4:6 years old, were presented one form each of the original and revised forms of the test. Results indicate the subjects achieved age equivalent scores significantly closer to their chronological ages on the PPVT-R.

Age Factors↗
PubMed1983

Biological expression of an Escherichia coli consensus sequence promoter and some mutant derivatives.

A prokaryotic consensus sequence promoter has been chemically synthesized and cloned in bacterial plasmid vectors. This designed sequence is biologically active and promotes efficient expression of the genes to which it is fused. It is an unusually strong promoter in vitro, capable of specifying multiple rounds of transcription even when there is a large molar excess of heparin present prior to the addition of RNA polymerase. These properties make this a useful sequence for the in vitro production of RNAs. A 2-base-pair spacer mutant and a -35 region transversion mutant have been created in vitro in the synthetic promoter by synthetic-DNA-mediated, site-specific mutagenesis. The spacer mutant has a marginal in vivo effect on promoter strength but virtually abolishes the in vitro heparin resistance. The -35 region transversion changes a highly conserved nucleotide into the statistically least preferred base. This mutation has no marked effect on in vivo or in vitro promoter strength.

Base Sequence↗
PubMed1983

Dual isotope Schilling test for measuring absorption of food-bound and free vitamin B12 simultaneously.

A prototype food-bound vitamin B12 (food-B12) absorption test has been developed in which 57Co-B12 was incorporated in vitro into egg yolk (yolk-B12) and served to volunteers in 50-g cooked portions together with toast and coffee for breakfast. Six hours later, 1 mg nonlabeled B12 was given intramuscularly and 24-hour urine was collected for radioactivity measurement. In separate tests, the absorption of yolk-B12 and crystalline 57Co-B12 was equally poor in patients with pernicious anemia. However, in patients with simple gastric achlorhydria and those who had undergone gastric surgery, the assimilation of yolk-B12 was impaired greatly, whereas the absorption of crystalline radio-B12 was normal. Egg yolk labeled with 58Co-B12 was administered together with crystalline 57Co-B12 in a dual isotope test with results similar to those obtained when the tests were prepared separately. This yolk-58Co-B12 test with its ability to detect malabsorption of food-B12 may be considered as an addition to the first part of the Schilling test.

Absorption↗
PubMed1981

Characterization of the Epstein-Barr virion-associated DNA polymerase as isolated from superinfected and drug-stimulated cells.

We reported previously that Epstein-Barr (EB) virions and detergent-treated nucleocapsids co-purified with significant amounts of DNA polymerase activity that did not resemble other known host or viral polymerases. We report here that this species of DNA polymerase activity is present at early times after infection in lymphocytes abortively lytically infected (superinfected) with EB virus. However, studies with [35S]methionine labeling suggest de novo synthesis of enzyme has not occurred. Conversely, drug-stimulated lymphocytes that synthesize EB viral late proteins and virions contain this species of polymerase to the virtual exclusion of all others. This EB viral polymerase shows a marked preference for nicked and gapped double-stranded rather than primed single-stranded DNA templates. Its processiveness as measured on primed theta X174 phage DNA template is lower than that of lymphocyte beta polymerase. The data reported here are consistent with the hypothesis that the EB virion-associated DNA polymerase is synthesized at late times in the viral life cycle as are other structural proteins but it plays an important role early after viral infection. It is known that mature herpes virion DNA (including that of EB virus) is nicked and gapped and we propose that virion polymerase repairs the viral DNA at an early stage in infection before viral DNA replication begins.

B-Lymphocytes↗
PubMed1978

Vitamin B12 assimilation from chicken meat.

Chicken meat labeled in vivo with radio-B12 was ingested by normal volunteers. The absorption, measured by the fecal excretion method, was similar to that reported for crystalline radiocyanocobalamin and for mutton, but exceeded that from eggs. Parenteral injection of 1000 microgram of nonlabeled vitamin B12 did not interfere with the absorption of the radio-B12 from the meat. The urinary radioactivities, which were as low as those after oral administration of radioactive hydroxocobalamin and vitamin B12 coenzyme, suggested that the radio-B12 was present in meat in coenzyme form or was converted into the stable hydroxoform during the process of cooking and digestion. Patients with pernicious anemia showed insignificant urinary radioactivities in a standardized urinary excretion test using chicken meat whereas subjects with simple gastric achlorhydria and partial gastrectomy had subnormal values although their absorption of crystalline radiocyanocobalamin was normal. The subnormal serum vitamin B12 concentration seen in these latter subjects may, therefore, be due to impaired assimilation of vitamin B12 from food.

Achlorhydria↗
PubMed1976

Inhibitory effect of eggs on vitamin B12 absorption: description of a simple ovalbumin 57Co-vitamin B12 absorption test.

Ovalbumin and egg yolks, mixed separately in vitro with radiocyanocobalamin (57 Co-vitamin B12), were served to normal volunteers in a cooked form. Ovalbumin, and to a lesser degree, egg yolks were observed to inhibit vitamin B12 absorption. This observation explains the rather poor assimilation of vitamin B12 from eggs labelled in vivo with 57 Co-vitamin B12.

Absorption↗
PubMed1975

Hepatocellular carcinoma and intermediate alpha1-antitrypsin deficiency (MZ phenotype).

A case history of a 16-year-old boy with hepatocellular carcinoma and an intermediate deficiency of alpha1-antitrypsin (MZ phenotype) is presented. Previous reports have suggested that hepatocellular carcinoma may be associated with the Z variant of antitrypsin and either a severe or intermediate antitrypsin deficiency. The present case is unusual because of the rather high level of the serum trypsin inhibitory capacity for an MZ heterozygote (1.633 units), which may be due to involvement of the liver by the tumor or to a recent partial hepatectomy. PAS-positive antitrypsin globules were seen in the primary tumor and in nodules metastatic to the mesentery, as well as in nonneoplastic portions of the liver. Hepatocellular carcinoma is another disease state that may occur preferentially in individuals with either severe or intermediate deficiencies of alpha1-antitrypsin.

Adolescent↗
PubMed1975

Vitamin B12 absorption from eggs.

The assimilation of 57Co B12 from in vivo labeled eggs was much inferior to that of a comparable amount of crystalline 57Co B12. Furthermore, the absorption varied with the form in which the eggs were served. Judged by the urinary excretion test and the plasma absorption of radioactivity the average absorption from boiled and fried eggs was more than twice that from scrambled whole eggs, but less than half that absorbed from crystalline 57Co B12.

Cobalt Radioisotopes↗