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Biomedical subjects

W J Harris

Publications and source records attributed to W J Harris.

At least 73 records · Page 4Linked to original sources
PubMed1983

Repair of 4-nitroquinoline-1-oxide-induced DNA damage in normal human cells and cells from classical and variant xeroderma pigmentosum.

The effect of 4-nitroquinoline-1-oxide (4NQO) upon 3 fibroblast cell lines derived from normal and xeroderma pigmentosum subjects have been compared. Excision-deficient XP cells (XP2BI), complementation group G, are nearly 200-fold more sensitive than normal cells to the lethal effect of 4NQO while XP variants (XP7TA), are 2-fold more sensitive. This cytotoxicity correlates with the levels of unscheduled DNA synthesis performed by the 3 cell lines. 4NQO causes a dose-related inhibition of DNA replication in all cell lines. However, newly replicated DNA synthesised immediately after treatment of cells with 4NQO is slightly smaller in XP7TA variant cells than in normal cells receiving the same dose of 4NQO, but DNA fragments in excision-deficient XP2BI are 50% smaller. It is likely that replicon elongation and joining together of newly replicated DNA fragments is dependent upon the excision of certain 4NQO-induced lesions, possibly normally repaired by a 'short-patch' repair process defective in XP2BI.

4-Nitroquinoline-1-oxide↗
PubMed1983

Use of corticosteroids as an adjuvant in terminal salpingostomy.

Between the years 1977 and 1980, 26 women underwent terminal salpingostomy with a standard operative procedure at Vanderbilt University Medical Center. The term pregnancy rate was 23%, and the ectopic pregnancy rate was 13%. Fourteen patients received dexamethasone perioperatively; and of these, 3 had term pregnancies (21%). Of the 12 patients not receiving dexamethasone, there were also three term pregnancies (25%). It is concluded from this small series that perioperative corticosteroids do not improve the term pregnancy rate for terminal salpingostomy.

Adult↗
PubMed1982

Newly synthesised DNA in ageing human cells in culture treated with 4-nitroquinoline-1-oxide.

Two lines of normal human embryonic lung fibroblasts, MRC-5 and F2002, were serially subcultured until senescence was attained. When cells were exposed to varying concentrations of the chemical carcinogen 4-nitroquinoline-1-oxide (4-NQO), the rate of DNA synthesis (as measured by thymidine incorporation) was reduced in a dose-dependent fashion in cells from both early and late passages. While the overall amount of incorporation was considerably lower in old cells, the extent of inhibition caused by 4-NQO treatment (relative to appropriate controls) was not related to culture age. Alkaline sucrose density gradient analysis of newly synthesised DNA from cells pre-treated with 4-NQO failed to detect any significant variation in the size of labelled DNA from cells examined immediately after incubation with radioactive thymidine. The shift of this labelled material to high molecular weight in 4-NQO-treated cells also showed no age-related difference.

4-Nitroquinoline-1-oxide↗
PubMed1982

Mutagenicity of azo dyes in the Salmonella/activation test.

The detection of certain bis-azo biphenyl dyes (Trypan blue, Evans blue and Congo red) by a modification of the standard Ames test protocol is reported. Detection of a mutagenic response required both the inclusion of FMN in S-9 mix and use of a static pre-incubation step prior to addition of top-agar and pouring in the usual manner. Evidence is presented to substantiate the proposal that use of this protocol provides optimal conditions for the two stages of activation required for the production of mutagenic metabolites from these dyes. These are (i) initial flavin-mediated (hepatic) azo reduction resulting in the formation of proximate mutagenic metabolites followed by (ii) the oxidative metabolism by S-9 resulting in the formation of ultimately mutagenic products.

Animals↗
PubMed1982

Factors affecting the response of N,N-dimethylaminoazobenzene in the Ames microbial mutation assay.

The mutagenicity of N,N-dimethylaminoazobenzene (DAB) is difficult to demonstrate in Ames' test. Usually there are specific requirements for activation by post-mitochondrial supernatant fluid (S-9) from Aroclor-treated rat livers and the pre-incubation modification of the test. Results from this laboratory suggest, however, that pre-incubation is not essential; also, that, contrary to published reports, concentrations of S-9 greater than 10% in S-9 mix do not reduce the mutagenic response. Induction of enzyme activity well above normal levels, on the other hand, is necessary, but this requirement can be substituted by the addition of norharman. If a competent S-9 mix is used, pre-incubation with or without shaking does not alter the response and supplementation with ATP or NADH similarly has no effect. It is concluded that interlaboratory differences in the ability to demonstrate DAB mutagenicity reflect differences in the level of induction of liver enzymes and, possibly, the concentration of endogenous co-factors.

Adenosine Triphosphate↗
PubMed1981

The effect of caffeine upon cell survival and post-replication repair of DNA after treatment of BHK 21 cells with either UV irradiation or N-methyl-n-nitrosoguanidine.

It has been found that in BHK 21 cells caffeine potentiates cell killing by both UV irradiation and N-methyl-N-nitrosoguanidine (MNNG). The potentiating effect is greater with UV than with MNNG. While non-toxic concentrations of caffeine inhibit the joining of newly-replicated DNA fragments into large molecular weight DNA (post-replication repair) after UV irradiation, they have no such effect after MNNG treatment. Furthermore, the joining of DNA fragments continues in the cells treated with 3 microgram/ml of MNNG, a dose which leads to less than 5% cell survival. While inhibition of the synthesis of large molecular weight DNA can explain the synergistic effect of caffeine upon cell survival after UV irradiation, it cannot explain the similar effect after MNNG treatment.

Animals↗
PubMed1978

DNA polymerases from Chlamydomonas reinhardii. Purification and properties.

Three DNA polymerase activities, A, B and C, were identified in extracts of exponentially growing synchronous cultures of Chlamydomonas reinhardii, and DNA polymerases A and B were characterized in detail. Both enzymes have the same binding affinity for DEAE-cellulose at pH 7.8, but can be distinguished from each other by their behaviour on phosphocellulose and DNA-agarose. 'Activated' calf thymus DNA was used as template, and the pH, K+ and bivalent-cation optima were measured. DNA polymerase A sediments at 5.3 S in glycerol gradients, with an apparent mol.wt. of 90000-100000. Polymerase B sediments between 8S and 10S in 100mM-KCl, the predominant species having an apparent mol.wt. of 200000. In 200mM-KCl, polymerase B dissociates to a single species, which sediments at 5.8S. A 3S species was found in aged preparations of both enzymes. The activity of polymerase B from cells harvested during nuclear DNA synthesis is twice that found in Chlamydomonas at other times during the cell cycle.

Cations↗
PubMed1978

DNA polymerases from Chlamydomonas reinhardii. Further characterization, action of inhibitors and associated nuclease activities.

The properties of three DNA polymerase species A, B and C, purified from Chlamydomonas reinhardii were compared. DNA polymerases A and B have Km values with respect to deoxyribonucleoside triphosphates of 19 micron and 3 micron respectively. DNA polymerase A is most active with activated DNA, but will also use native DNA and synthetic RNA and DNA templates with DNA primers. DNA polymerase B is also most active with activated DNA, but will use denatured DNA and synthetic DNA templates. It is inactive with RNA templates. DNA polymerase B is completely inactive in the presence of 100 micron-heparin, which has no effect on DNA polymerase A activity. Heparin dissociates DNA polymerase B into subunits that are still catalytically active, but which heparin inhibited. DNA polymerase B possesses deoxyribonuclease activity that is inhibited by 5 micron-heparin, suggesting that the deoxyribonuclease is an integral part of the DNA polymerase moiety. DNA polymerase A is devoid of nuclease activity. DNA polymerase C is similar to DNA polymerase B in all these properties, though it is more active with RNA primers and has greater heat-sensitivity.

Chlamydomonas↗
PubMed1977

A deoxyribonuclease from Chlamydomonas reinhardii. 1. Purification and properties.

A deoxyribonuclease has been purified more than 2000-fold from the green algae, Chlamydomonas reinhardii. The enzyme is most active on denatured DNA. Optimum activity is at pH 8.5, in 80 mM Tris-HCl buffer and 2 mM CaCl2. Other divalent cations can replace Ca2+ with varying lower efficiency. EDTA and inorganic phosphate are strongly inhibitory, while ATP and high concentrations of 2-mercaptoethanol are slightly inhibitory. The molecular weight is approximately 35 000, the Stokes radius is 2.7 nm, and the sedimentation coefficient 2.8 S. It is a single polypeptide chain, and the frictional ratio of 1.27 suggests it is only slightly asymetrical. The isoelectric point is 9.5. This enzyme has been termed exonuclease 1.

Adenosine Triphosphate↗
PubMed1977

A deoxyribonuclease from Chlamydomonas reinhardii. 2. Substrate specificity, mode of action and products.

A deoxyribonuclease purified Chlamydomonas reinhardii has been shown to be specific for single-stranded DNA. The enzyme is most active on thermally denatured DNA, but also degrades single-stranded termini from double-stranded DNA. The enzyme has no effect on single-stranded or double-stranded intact circular phiX174DNA, suggesting that it requires DNA termini for activity. DNA is digested progressively to oligonucleotides and then mononucleotides. The product of the reaction is nucleoside 5'-monophosphates. The enzyme has no effect on RNA, nor does it possess phosphatase or phosphodiesterase activity. No specificity was demonstrated for phosphate or hydroxyl groups at either the 5' or 3' termini of DNA. The enzyme may be able to initiate hydrolysis at either the 3' or the 5' termini, since radioactivity was released more rapidly from 5' and 3' termini than from bulk DNA. The enzyme has been tentatively named Chlamydomonas reinhardii exonuclease 1.

Chlamydomonas↗
PubMed1977

An investigation of relationships between teachers' ratings of behavior and children's personality traits.

This study examined the relationships between teachers' ratings of children's behavior on the Behavior Problem Checklist and children's self-reported personality source traits on age-appropriate Personality Questionnaires. The sample consisted of 254 children from first through eighth grades and 13 teachers in a rural Maine elementary school. Analysis of the data revealed that teachers' ratings and children's self-reports in grades four through six agreed more frequently about problematic behavior than did children's self-reports and teachers self-ratings in grades one through three and seven and eight. In general, the study (1) supported the validity of teacher judgments made with the Behavior Problem Checklist, (2) demonstrated the critical need for more than one perspective when identifying and defining maladaptive behavior potentially indicative of emotional disturbance, and (3) suggested the need to increase the accuracy of teachers' perceptions and evaluations of children's behavior.

Adolescent↗