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Biomedical subjects

J S Knight

Publications and source records attributed to J S Knight.

15 recordsLinked to original sources
PubMed2000

The bicyclomycin sensitivities of 38 bicyclomycin-resistant mutants of transcription termination protein rho and the location of their mutations support a structural model of rho based on the F(1) ATPase.

A total of 38 bicyclomycin-resistant mutants of Escherichia coli transcription termination protein Rho have been isolated. The locations of their mutations identify the ATP-binding region as the functional domain inhibited by bicyclomycin. Strains containing the S266C, S266A and L208R Rho mutations are very resistant to bicyclomycin in vivo. In a similar way, the mutant Rho proteins containing these mutations are very resistant to bicyclomycin in vitro. These data suggest that Ser266 and Leu208 might make direct contact with the antibiotic. These two residues are close to each other in the tertiary structure of a model of Rho based on the alpha and beta subunits of the F(1) ATPase, supporting the validity of the model. The strain containing the G337S Rho mutation also has high bicyclomycin resistance, and the proximity of L208, S266 and G337 in the quaternary structure of the Rho model has enabled a candidate bicyclomycin-binding pocket to be delineated. As a whole, the bicyclomycin sensitivities of the mutants are consistent with the locations of their respective mutations in the model of Rho based on the F(1) ATPase, therefore supporting the emerging consensus model of Rho structure.

Adenosine Triphosphate↗
PubMed2000

Decrease of phosphoribulokinase activity by antisense RNA in transgenic tobacco: definition of the light environment under which phosphoribulokinase is not in large excess.

To test the hypothesis that the contribution of phosphoribulokinase (PRK) to the control of photosynthesis changes depending on the light environment of the plant, the response of transgenic tobacco (Nicotiana tabacum L.) transformed with antisense PRK constructs to irradiance was determined. In plants grown under low irradiance (330 micromol m(-2) s(-1)) steady-state photosynthesis was limited in plants with decreased PRK activity upon exposure to higher irradiance, with a control coefficient of PRK for CO2 assimilation of 0.25 at and above 800 micromol m(-2) s(-1). The flux control coefficient of PRK for steady-state CO2 assimilation was zero, however, at all irradiances in plant material grown at 800 micromol m(-2) s(-1) and in plants grown in a glasshouse during mid-summer (alternating shade and sun 300-1600 micromol m(-2) s(-1)). To explain these differences between plants grown under low and high irradiances, Calvin cycle enzyme activities and metabolite content were determined. Activities of PRK and other non-equilibrium Calvin cycle enzymes fructose-1,6-bisphosphatase, sedoheptulose-1,7-bisphosphatase and ribulose-1,5-bisphosphate carboxylase-oxygenase were twofold higher in plants grown at 800 micromol m(-2) s(-1) or in the glasshouse than in plants grown at 330 micromol m(-2) s(-1). Activities of equilibrium enzymes transketolase, aldolase, ribulose-5-phosphate epimerase and isomerase were very similar under all growth irradiances. The flux control coefficient of 0.25 in plants grown at 330 micromol m(-2) s(-1) can be explained because low ribulose-5-phosphate content in combination with low PRK activity limits the synthesis of ribulose-1,5-bisphosphate. This limitation is overcome in high-light-grown plants because of the large relative increase in activities of sedoheptulose-1,7-bisphosphatase and fructose-1,6-bisphosphatase under these conditions, which facilitates the synthesis of larger amounts of ribulose-5-phosphate. This potential limitation will have maintained evolutionary selection pressure for high concentrations of PRK within the chloroplast.

Light↗
PubMed2000

Strengths of composite bonded to base metal alloy using dentin bonding systems.

STATEMENT OF PROBLEM: Many different bonding systems are currently available that may be used to bond composite to base metal alloy. PURPOSE: This study measured and compared bond strengths of composite with a base metal alloy using 8 modern dentin bonding systems. MATERIAL AND METHODS: Base metal alloy buttons were imbedded in acrylic and ground with 120, 400, and 600 grit sandpaper, respectively. Metal surfaces were air abraded for 5 seconds with 50 microm aluminum oxide, washed for 5 seconds under running tap water, then dried with compressed air. Specimens were arbitrarily divided into 8 groups of 10 specimens. Each group was treated with 1 of 8 dentin bonding regimens. A hybrid composite (Herculite) was placed onto the treated metal surface and light polymerized. Specimens were incubated at 37 degrees C in distilled water for 2 hours. Shear bond strengths were measured and the collected data subjected to an ANOVA, followed by multiple t -tests. RESULTS: All-Bond 2 exhibited the highest mean shear bond strength and Panavia 21 with primer had the lowest in the tests conducted. CONCLUSION: All-Bond 2 demonstrated significantly higher shear bond strengths over all materials tested, except 3M Single Bond and Optibond FL. No significant difference was noted between the single component and the multicomponent bonding systems.

Analysis of Variance↗
PubMed1999

Effects of handpiece lubrication on resin-based composite bond strength to enamel.

PURPOSE: To evaluate the effects of handpiece lubrication on the bond strengths of resin-based composite (RBC) to enamel using two different bonding systems. MATERIALS AND METHODS: Sixty extracted noncarious human maxillary incisors were imbedded in acrylic resin tray material with the facial surfaces exposed. 320 grit sandpaper was used to create a flat surface of enamel. The embedded teeth were randomly divided into two bonding systems groups: half used All-Bond 2 and half used OpiBond FL. Within these two groups the teeth were again randomly divided into three subgroups: Dry: 10 teeth prepared with a sterilized unlubricated handpiece; Lube & Run: 10 teeth prepared with a handpiece that was lubricated and run for 30 seconds prior to use; Lube: 10 teeth prepared with a handpiece that was lubricated and not run prior to its use. The enamel was prepared by lightly roughening with a medium grit diamond in the respective handpieces. The preparations were etched for 15 s with 32% phosphoric acid, rinsed with water for 5 s, and dried with compressed air for 5 s. Either bond system was applied and light-cured. A hybrid RBC was placed and light-cured for 60 s. The teeth were stored in water at 37 degrees C 1 week. Shear bond strengths were measured and the collected data subjected to an ANOVA followed by a Tukey's and Bonferroni t-test were performed. RESULTS: The Dry group and the Lube & Run group had stronger mean shear strengths than did the Lube group. The difference between the mean shear strengths for the Dry group and the Lube & Run group was not statistically significant (P < 0.05). A significant difference was found between the Dry group and the Lube group and between the Lube & Run group and the Lube group (P < 0.05). The mean shear strength for All-Bond 2 was higher than for OptiBond FL (P = 0.0054).

Analysis of Variance↗
PubMed1997

Azide-sensitive thylakoid membrane insertion of chimeric cytochrome f polypeptides imported by isolated pea chloroplasts.

Post-translational integration of cytochrome f into thylakoid membranes was observed after import by isolated pea chloroplasts of a chimeric protein consisting of the presequence of the small subunit of ribulose 1,5-bisphosphate carboxylase fused to the cytochrome f precursor. Import of a similar chimeric protein lacking the C-terminal 33 amino acid residues resulted in a soluble cytochrome f protein in the thylakoid lumen, indicating that the C-terminal region contains a stop-transfer sequence for membrane integration. Azide inhibited the insertion of cytochrome f into the thylakoid membrane, whereas the ionophores nigericin and valinomycin had little effect on membrane insertion. The precursor of the 33 kDa protein, but not the 23 kDa protein, of the photo-system II oxygen-evolving complex inhibited the thylakoid insertion of cytochrome f, suggesting competition for a component of the transport pathway. These experiments suggest that the post-translational insertion of cytochrome f into the thylakoid membrane uses a SecA-dependent pathway.

Azides↗
PubMed1996

Manipulating photosynthesis.

The levels of individual photosynthetic proteins can be independently decreased by the Agrobacterium-mediated transformation of plants with antisense RNA constructs. Protocols for the introduction of such constructs into Agrobacterium, the Agrobacterium-mediated transformation of tobacco leaf disks, and the screening and analysis of the transgenic plants produced are described.

Agrobacterium tumefaciens↗
PubMed1995

The N-terminal hydrophobic region of the mature phosphate translocator is sufficient for targeting to the chloroplast inner envelope membrane.

To locate the sequence required for directing the phosphate translocator to the chloroplast inner envelope membrane, a series of chimeric proteins constituting parts of the phosphate translocator and the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase, which is normally located in the stroma, has been produced. Reciprocal exchanges of the presequences and mature sequences of the phosphate translocator and the small subunit indicated that the phosphate translocator presequence contains stromal targeting information and that the mature protein is responsible for inner envelope membrane targeting. Chimeric proteins containing the N-terminal 46 amino acid residues of the phosphate translocator were directed to the inner envelope membrane. Subdivision of this region into its composite hydrophilic and hydrophobic regions showed that the hydrophobic region alone, which consists of amino acid residues 24 to 45, was able to direct the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase to the inner envelope membrane.

Base Sequence↗
PubMed1994

Expression of genes encoding the tobacco chloroplast phosphate translocator is not light-regulated and is repressed by sucrose.

A cDNA encoding the complete precursor of the phosphate translocator of the chloroplast inner envelope membrane has been isolated from a tobacco leaf (Nicotiana tabacum cv. Samsun) lambda gt 11 library. The tobacco cDNA is 1546 bp in length and encodes a precursor protein of 401 amino acid residues with a deduced molecular weight of 43705. A putative processing site between Ala-73 and Ala-74 of the precursor protein is suggested by comparison with the N-terminal sequences of the pea and spinach proteins. Removal of the transit peptide produces the mature protein of 328 amino acid residues with a molecular weight of 36038. Southern blot analysis suggests there is probably one copy of the phosphate translocator gene in the pea haploid genome and two copies in the tobacco haploid genome, one derived from each ancestral parental genome. Messenger RNAs essentially equivalent in size to the cDNAs (approx. 1.6 kb) were detected in extracts of all organs examined from tobacco and pea, including leaves, stems, sepals, petals, seed-pods, tendrils and roots. An immunochemically related protein of a similar size to the phosphate translocator was detected in the equivalent pea organs. The levels of both mRNA and protein in non-photosynthetic organs were lower than those in photosynthetic organs. Tobacco phosphate translocator mRNA was present at high levels in etiolated tissue and did not increase significantly after 24 h illumination. Germination and growth of tobacco seedlings in the presence of sucrose caused a 3.3-fold decrease in the level of the phosphate translocator mRNA.

Amino Acid Sequence↗
PubMedDate not supplied

A matrix solution for severly broken-down teeth.

A technique is described for preparation of a dead-soft copper band matrix for tooth restorations. Such a matrix is particularly useful in the restoration of teeth with significant variation in occlusogingival height.

Dental Amalgam↗
PubMedDate not supplied

The heat sink and its relationship to reducing heat during pin-reduction procedures.

When self-threading pins are used in the restoration of teeth, the heat generated by cutting these pins to the correct length may traumatize the pulp. This study evaluated cotton forceps and a mosquito hemostat used as a heat sink and at different positions on the pin to determine any change in heat transferred to the tooth. Three hundred self-threading pins (Whaledent TMS System: 100 each of the Regular, Minim, and Minikin sizes) were inserted into freshly extracted teeth and sectioned. The temperature change at the apical end of the pin was measured using a thermistor probe. The results indicated that metal supporting instruments can be effective in reducing heat transferred to the apical aspect of the pin during pin reduction.

Dental Pins↗