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Biomedical subjects

D J Beck

Publications and source records attributed to D J Beck.

At least 37 records · Page 2Linked to original sources
PubMed1989

Mass spectral investigations on trichothecene mycotoxins. VIII--Thermospray ionization and collisionally activated dissociation of macrocyclic trichothecenes.

Several structurally similar, biologically active macrocyclic trichothecenes were ionized under thermospray conditions followed by collisionally activated dissociation of the ammonium adducts. Most of the observed daughter ions were formed by bond cleavage at the exocyclic ester bridges. Compounds with similar ester bridges formed several common daughter ions and underwent similar neutral losses. Fragmentation pathways proposed for the dissociation of the adducts were confirmed from the corresponding neutral loss spectra. Simple experiments designed for the sequential monitoring of the characteristic daughter ions were used for the rapid, direct and accurate analysis of macrocyclic trichothecenes in real samples. The primary drawback of the method is its inability to distinguish between isomers.

Chemical Phenomena↗
PubMed1987

Anthropometry and leisure activities of some Dunedin children aged 11 to 13, 1976 and 1984.

A study of weight, skinfold thickness and leisure-time activities of a group of Dunedin children aged 11 to 13, conducted in 1976, was repeated in 1984. Both weight and skinfold thickness were materially lower in the 1984 study, the difference being particularly marked in the girls. Both boys and girls spent significantly more time playing sport on Saturday in 1984 than in 1976 and twice as many walked or rode a bicycle to school. The time spent watching television was a little less in 1984; playing videogames is much more common among boys than girls.

Adolescent↗
PubMed1987

Repair of plasmid DNA damaged in vitro with cis- or trans-diamminedichloroplatinum(II) in Escherichia coli.

Plasmid pBR322 was modified in vitro with the antitumor compound cis-diamminedichloroplatinum(II) (cis-DDP) or the isomeric trans-DDP. The numbers of platinum adducts were determined by atomic absorption spectrophotometry. DNA-repair-proficient and various DNA-repair-deficient (uvrB, uvrD, recB and recA) strains of Escherichia coli were transformed by the damaged plasmids and the ratios of the transformation frequencies of cells by damaged plasmids relative to those by untreated plasmids were determined. Results of transformation assays indicated that the uvrB gene function was essential for repair of plasmid DNA damaged with cis-DDP. A functional recA gene product seemed to be of minor importance for repair of plasmids damaged with cis-DDP. trans-DDP had a different effect on plasmid DNA. trans-DDP-modified DNA was better able to transform cells than cis-DDP-modified DNA, and the DNAs appeared to be repaired differently. Prior induction of SOS functions increased the survival of plasmids treated with cis-DDP in wild-type and uvrD mutants, but did not increase the survival of plasmids damaged with trans-DDP in these strains. In in vitro repair experiments, plasmid DNA modified with cis-DDP was more readily incised by the UVRABC excinuclease than that modified with trans-DDP.

Cisplatin↗
PubMed1985

Reactions of the UVRABC excision nuclease with DNA damaged by diamminedichloroplatinum(II).

Mutants of Escherichia coli, which are blocked in excision repair (uvrA6, uvrB5, or uvrC34) are exceptionally sensitive to the antitumor drug cis-Pt(II)(NH3)2Cl2 (cis-DDP) but not the trans isomer. Plasmid DNA, damaged by either the cis or trans compound and treated with the UVRABC excision nuclease was cut as shown by conversion of supercoiled DNA to relaxed forms. All three protein products of the uvrA, uvrB, and uvrC genes were required for incision. End-labeled fragments damaged with cis-DDP and reacted with the UVRABC nuclease were cut at the 8th phosphodiester bond 5' and at the 4th phosphodiester bond 3' to adjacent GG's. DNA treated with trans-DDP was not cut appreciably at adjacent GG's by the repair enzyme as subsequent analysis of reaction products after enzyme digestion gave a pattern similar to those obtained with control untreated fragments. The results indicate that the UVRABC nuclease may promote cell survival by the removal of adjacent GG's which are crosslinked by cis-Pt(II)(NH3)2Cl2.

Base Sequence↗
PubMed1984

The effects of cis-platinum (II)diamminodichloride, UV light and N-methyl-N'-nitro-N-nitrosoguanidine on Escherichia coli:plasmid mediated resistance to mutagens.

Protease deficient recA431 mutants of Escherichia coli are defective in their capacity for induction of SOS responses and were intermediate in their sensitivities to ultraviolet light (UV) and cis-platinum (II) diamminodichloride (cis-PDD). Survival after treatment determined as colony forming ability was greater in rec+ strains and decreased in recA13 mutants which are defective in both recA proteolytic and recombination capabilities. In contrast, recA431 mutants were as sensitive to N-methyl-N'-nitro-N-nitrosoguanidine (NTG) as the recA13 cells. When cells carried either the pKM101 or N3 plasmid, survival after treatment with the three mutagens was increased. Presence of these plasmids in cells also resulted in hypermutagenicity as indicated by reversion of the argE3 mutation using a modified Ames test. Mutagenesis by NTG and cis-PDD was increased, as was survival of cells treated with UV light, cis-PDD and NTG in both recA+ and recA431 (protease deficient) strains. No plasmid mediated enhancement of mutagenesis or cell survival was observed in recA13 mutants. Thus, the ability of the plasmids to enhance cell survival and mutagenesis was dependent on recombination proficiency of the recA gene product and not its regulatory proteolytic activity. Unlike UV or NTG, presence of one of these plasmids was needed to detect reversion of the argE3 mutation by cis-PDD.

Cisplatin↗
PubMed1984

Relationship between fluoridation and socioeconomic status on dental caries experience in 5-year-old New Zealand children.

This article examines the relationship between fluoridation and socioeconomic status on caries experience, as measured by the dmf index, in 5-yr-old New Zealand children in the city of Dunedin (fluoridated in 1967) and in adjacent non-fluoride communities. The children were subdivided into six socioeconomic status groups (SES 1, professional and managerial-SES 6, unskilled workers), but then for simplicity they were combined to form three groups. A two-way analysis of variance demonstrated that interaction between fluoride history and socioeconomic status was not significant. In all three SES groups, dmf was higher in non-fluoride communities, but the difference was significant only in SES group (5&6) (P less than 0.01). Caries experience increased with decreasing socioeconomic status in both fluoride and non-fluoride communities, but this effect was only significant between SES groups (1&2) and (3&4) in the fluoridated community (P less than 0.05), and between SES groups (3&4) and (5&6) in non-fluoride communities (P less than 0.01). These results are compared with those of similar studies, and it is concluded that so far, the relationship between fluoridation and socioeconomic status on caries experience remains equivocal. A note of caution is sounded regarding the interpretation of such results, and the difficulties faced when comparing studies is discussed.

Analysis of Variance↗
PubMed1978

A comparison of WHO periodontal status index with the periodontal and oral hygiene indices.

Examination of 2,138 subjects, aged 15-65+ years, was carried out by calibrated examiners using mirrors and fibre optic illumination. Each subject was scored by the Periodontal Status Index, PSI (WHO Oral Health Surveys), Periodontal Index, PI (Russell) and the Oral Hygiene Index, OHI (Greene & Vermillion). For the PSI, PI and OHI all scores were age-dependent with the exception of soft deposits in PSI and OHI, which were age-independent. The advantages of the PSI system were considered to be the ease of scoring and the opportunity to assess treatment requirements, in terms of time, at the public health service level. Disadvantages were lack of quantitation, difficulties of diagnosis of intense gingivitis, and localized and general conditions. The PI and OHI systems provided a more objective, quantitative and sensitive basis of scoring than the PSI. Statistical tests showed the respective indices are associated and measuring the same kind of criteria. Examiner calibration and consistency were similar for both scoring systems.

Adolescent↗
PubMed1976

Transactions of an international conference. Worldwide concern: better dental care for more people. An international collaborative study. How oral surveys were conducted.

A special form and field manuals defining examination criteria were prepared for recording the following: 1. Number of teeth present both primary and permanent 2. Periodontal disease (a) Oral hygiene using the simplified oral hygiene index. (b) Periodontal condition using a modified P.I. index. (c) Periodontal treatment requirements. 3. Dental caries The DMF index was used with separate coding for filled or crowned teeth having additional primary or secondary decay. 4. Dento facial anomalies Both treatment need and treatment status were recorded. 5. Prosthetic status Possession and requirements for partial or full dentures and bridges were recorded for the age groups 13-14 and 35-44. 6. Oral pathology Pathological conditions of the gingiva and oral mucosa. 7. Need for immediate attention Conditions causing or likely to cause pain or danger to general health unless immediate treatment was given. The recording was carried out using fibre optic illumination, disposable mirrors and sickle probes. X-rays were not utilized. Two roving epidemiologists first established reproducible criteria and then calibrated the local examiners. Re-calibration took place at intervals and repeat examinations of a small sample population ensured reproducibility of recordings. The completed charts were sent to the WHO Oral Health Unit where they were edited and the data transferred to computer tape for analysis. For the present reports three variables--number of carious teeth, caries treatment/need ratio and number of teeth with gingivitis were selected for special study.

Adolescent↗
PubMed1975

Mutagenic properties of cis-plantinum(II)diammino-dichloride in Escherichia coli.

cis-Platinum (II)diamminodichloride (PDD), an anti-tumor agent, induced auxotrophic mutations in Escherichia coli, some of which were reverted to prototrophy by exposure to PDD, 2-aminopurine (2-AP), and N-methyl-N'-nitro-N-mitrosoguanidine (NTG), but not ICR derivatives. Similarly, various 2-AT-, NTG-, and ultraviolet light-induced auxotrophs were reverted to prototrophy by PDD. Some PDD-induced auxotrophs carried nonsense mutations and others could be phenotypically suppressed growth with streptomycin. Although these findings suggest that PDD promotes base substitutions, this mutagen may also cause base subtractions because (like NTG) it induced, at reduced frequency, reversion to prototrophy of certain ICR-induced auxotrophs. Isomeric trans-platinum (II)diamminodichloride, which lacks anti-tumor activity, was an ineffective mutagen. Near-optimal conditions for PDD-induced mutagenesis entailed prolonged cultivation with low levels of mutagen where the frequency of forward mutation to auxotrophy was 10-3 and that of a selected trp isolate to prototrophy was 10-2.

Acridines↗