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Biomedical subjects

C K Ross

Publications and source records attributed to C K Ross.

15 recordsLinked to original sources
PubMed1992

Formation of heterodimers of human-immunodeficiency-virus-type-1 reverse transcriptase by recombination of separately purified subunits.

Human-immunodeficiency-virus-type-1 reverse transcriptase exists in virions as a heterodimer of a M(r) 66,000 subunit and its C-terminally truncated form of M(r) 51,000, but, when expressed as a recombinant M(r) 66,000 protein, a mixture of heterodimers and homodimers results which co-purify by most conventional techniques. We describe a method of hydrophobic chromatography which gives baseline separation of these two forms of the protein. This method has been applied to purify heterodimers formed by recombination of separately expressed and purified M(r) 66,000 and 51,000 subunits, resulting in significantly more homogeneous heterodimer preparations. The recombined heterodimer showed similar kinetic properties and RNase H activity to the standard heterodimer and a specific activity significantly higher than the original homodimer of the M(r) 66,000 protein. Heterodimers having greater asymmetry have also been prepared by recombining Mr 66,000 subunits containing single-point or deletion mutations, with wild-type M(r) 51,000 subunits, and the resulting heterodimers analysed.

Chromatography, Gel↗
PubMed1992

Evaluation of a psychological treatment package for treating pain in juvenile rheumatoid arthritis.

We examined the utility of psychological treatment procedures for children with high levels of pain associated with juvenile rheumatoid arthritis (JRA). By the use of a multiple baseline across subjects design, four children were assigned to an immediate treatment group, and four children to a delayed treatment group. The six-session treatment included relaxation training, electromyogram, and thermal biofeedback for the child; mothers were trained in the use of behavioral techniques for managing physical therapy and school attendance. Visual inspection of the data indicates small changes on children's self-reported pain diary scores for mean pain and ratings of high (greater than 5 on a 10-point visual analogue scale) pain periods, with 50% to 62% showing at least a 25% reduction in pain immediately after treatment, and 62% to 88% showing a 25% reduction by 6-month follow-up. Maternal reports of changes paralleled those of the children. Comparisons of Mann-Whitney U-tests conducted pre- and posttreatment indicated no differences for children's ratings of mean pain or +5 pain ratings between the immediate and delayed treatment groups; greater improvement for the immediate treatment group was noted on maternal reports of both mean pain (p < 0.05) and +5 pain (p < 0.5) ratings. The reduction of pain reports from pretreatment to follow-up was significant for children's mean pain (p = 0.02), +5 pain ratings (p = 0.02), and mother's reports of mean pain (p = 0.03) and +5 pain periods (p = 0.01). Maternal reports of the number of pain-related behaviors that the child exhibited also declined (p < 0.05). No reduction in physical therapist's ratings of pain during evaluation were noted. No increases in maternal reports of child's psychological adjustment problems were reported following treatment. Results provide modest support for the use of psychological interventions with patients with JRA.

Adolescent↗
PubMed1991

Rapid purification and characterisation of HIV-1 reverse transcriptase and RNaseH engineered to incorporate a C-terminal tripeptide alpha-tubulin epitope.

The C-termini of p66 and p51 forms of HIV-1 reverse transcriptase have been engineered to contain a Glu-Glu-Phe sequence recognized by a monoclonal antibody to alpha-tubulin, YL1/2. Mutated RTs were purified in a single step using peptide elution from columns of immobilized YL1/2. The known sequence requirements of the YL1/2 epitope are consistent with protein eluting from the column with an intact C-terminus. Kinetic parameters of these mutated RTs are essentially unchanged from wild-type enzyme. The p15 RNaseH domain has been purified using this method and shown to have low enzyme activity compared to the parental p66 subunit.

Amino Acid Sequence↗
PubMed1991

The dynamic instability of microtubules is not modulated by alpha-tubulin tyrosinylation.

The tyrosinylation of chick brain alpha-tubulin and the effects of the tyrosinylation status on the assembly and dynamic instability of chick brain MAP2:tubulin microtubule protein have been examined. Each of the eight major alpha-isotypes can be tyrosinylated in vitro, irrespective of whether a C-terminal tyrosine is genetically encoded. The extent of tyrosinylation is however limited to congruent to 0.3 mol.mol-1. The tyrosinylation status (0 vs. 0.3 mol.mol-1) has no effect on either the assembly kinetics of chick brain microtubule protein or on the rate of length redistribution following assembly and shearing. It is therefore unlikely that the tyrosinylation status directly affects the intrinsic stability of assembled microtubules since the rate of length redistribution is both a sensitive assay and a function of the kinetic parameters governing dynamic instability.

Animals↗
PubMed1991

Preliminary examination of the reliability and relation to clinical state of a measure of low vision patient functional status.

An evaluation of the reliability and relation to clinical state of a measure of low vision patient functional status was conducted. The measure included discrete tasks aggregated into three different areas: identifying objects, reading, and daily/leisure activities. Data were obtained retrospectively from case records of 247 low vision patients and 144 complete cases were used for statistical analyses. Evidence of reliability was found with coefficient alpha scores for the three areas ranging from 0.90 to 0.96. Significant relations between functional status and clinical states (acuity, contrast sensitivity, and visual field) were found with R2 values ranging from 0.39 to 0.58, p less than 0.001.

Activities of Daily Living↗
PubMed1990

The role of expectations and preferences in health care satisfaction of patients with arthritis.

Studies of patient satisfaction have typically been conducted in general patient populations with little attention to patients suffering from specific illnesses. The purpose of this article is to review literature and raise issues relevant to the satisfaction of patients with chronic arthritis. Individuals suffering from a chronic illness such as arthritis may be different from others who seek medical care in their expectations, what they expect from care, and preferences, what they want from care. These differences may occur because patients with chronic arthritis have greater experience with care seeking and increasing recognition of the potential for poor disease outcomes in spite of adequate care. Literature from marketing research and health care which suggests that both expectations and preferences influence satisfaction with care will be reviewed. Then specific hypotheses about expectations and preferences of patients with chronic arthritis will be proposed. Recommendations for future studies of arthritis patient expectations and preferences will be made.

Arthritis↗
PubMed1989

A direct comparison of water calorimetry and Fricke dosimetry.

Considerable effort has been devoted to measuring the absorbed dose to water using water calorimetry. Most of these efforts have been hampered by a lack of adequate knowledge of the heat defect of water. We argue that there is now sufficient information to establish with considerable confidence the heat defect of high-purity water containing various dissolved gases. For the present work we used water saturated with a 50/50 mixture of H2 and O2 gases, for which the heat defect is calculated to be -2.1%. As a test of this assignment, we have compared the absorbed dose to water as measured using water calorimetry with that obtained from Fricke dosimetry. The water calorimeter consisted of a small sealed vessel containing 100 ml of stirred water saturated with a 50/50 mixture of H2 and O2 gases. It was irradiated with 20 MV x-rays at a dose rate of about 0.4 Gy s-1. The same vessel was then filled with Fricke dosemeter solution, and irradiated under identical conditions. Our Fricke dosimetry is based on the Svensson and Brahme value of epsilon G (3.515 x 10(-3) 1 cm-1 J-1) and agrees to within 0.2% with the dose to water for 60Co gamma-rays obtained via graphite calorimetry. We find that for 20 MV x-rays, the dose to water determined by water calorimetry is 1.006 +/- 0.004 times the dose determined by Fricke dosimetry. Within 0.6(+/- 0.4)%, this result supports the calculated heat defect of -2.1% for water saturated with a 50/50 mixture of H2 and O2 gases.

Calorimetry↗
PubMed1989

Validity of reported pain as a measure of clinical state in juvenile rheumatoid arthritis.

Reported pain is one valid indicator of clinical state which should be used in the assessment and management of children with juvenile rheumatoid arthritis. Parents' reports of children's pain for 101 children with juvenile rheumatoid arthritis differed significantly by type of juvenile rheumatoid arthritis. When multiple regression was used separately for pauciarticular and polyarticular classifications of juvenile rheumatoid arthritis a measure of clinical state, which reflected joint activity, morning stiffness, and overall disease activity as rated by the doctor, had a significant and independent effect upon pain reported by parents. The child's age was not significantly related to the pain reported by parents. Children's pain reports did not differ significantly between older and younger children.

Adolescent↗
PubMedDate not supplied

The role of humidity and other correction factors in the AAPM TG-21 dosimetry protocol.

A detailed derivation is presented of the formulas required to determine Ngas and Dmed in the AAPM TG-21 dosimetry protocol. This protocol specifies how to determine the absorbed dose in an electron or photon beam when using exposure or absorbed dose calibrated ion chambers. It is shown that the expression given in TG-21's recent letter of clarification is incorrect. Accounting for humidity correctly increases, by 0.4%, all absorbed dose determinations using an exposure calibrated ion chamber. Taking into account other correction factors in the equation for exposure could also have varying, but significant effects (possibly over 1%). These are the stem scatter correction, the axial nonuniformity correction and the electrode correction for electrodes made of different materials from the wall. Attention is drawn to differences in the definitions of the exposure and absorbed dose calibration factors, Nx and ND, respectively, as supplied by the NBS and the NRCC.

Humans↗
PubMedDate not supplied

Forward-directed bremsstrahlung of 10- to 30-MeV electrons incident on thick targets of Al and Pb.

Bremsstrahlung spectra from thick targets of Al and Pb have been measured absolutely (photons per incident electron) along the beam axis for electrons of 10-, 15-, 20-, 25-, and 30-MeV incident energy. The spectra have a 220-keV low-energy cutoff. The targets were cylinders with nominal thicknesses of 110% of the electron CSDA range. A thin transmission detector, calibrated against a toroidal current monitor, was placed upstream of the target to measure the beam current. The spectrometer was a 20-cm diameter by 25-cm-long cylindrical NaI detector. Measured spectra were corrected for pile-up, background, detector response, detector efficiency, attenuation in materials between the target and detector and the collimator effect. Spectra were calculated using the EGS4 Monte Carlo system for simulating the radiation transport. The simulation model included the small amount of material upstream of the target. This material contributed about 40% of the spectrum, but its presence or absence had little effect on the calculated bremsstrahlung yield. The shapes of the measured and calculated spectra were in excellent agreement. The ratio of the total number of photons in each measured spectrum to those in the corresponding calculated spectrum varied from 0.97 +/- 0.06 to 1.12 +/- 0.06, depending largely on the atomic number of the target. Absolute spectral measurements in the literature agreed with our calculations of spectral shape but showed a range of +/- 30% in the number of photons per incident electron relative to the calculated values, which is contrary to our result.

Aluminum↗
PubMedDate not supplied

Angular distribution of bremsstrahlung from 15-MeV electrons incident on thick targets of Be, Al, and Pb.

Bremsstrahlung spectra from thick cylindrical targets of Be, Al, and Pb have been measured at angles of 0 degrees, 1 degree, 2 degrees, 4 degrees, 10 degrees, 30 degrees, 60 degrees, and 90 degrees relative to the beam axis for electrons of 15-MeV incident energy. The spectra are absolute (photons per incident electron) and have a 145-keV lower-energy cutoff. The target thickness were nominally 110% of the electron CSDA range. A thin transmission detector, calibrated against a toroidal current monitor, was placed upstream of the target to measure the beam current. The spectrometer was a 20-cm-diam by 25-cm-long cylindrical NaI detector. Measured spectra were corrected for pile-up, background, detector response, detector efficiency, attenuation in materials between the target and detector and collimator effects. Spectra were also calculated using the EGS4 Monte Carlo system for simulating the radiation transport. There was excellent agreement between the measured and calculated spectral shapes. The measured yield of photons per incident electron was 9% and 7% greater than the calculated yield for Be and Al, respectively, and 2% less for Pb, all with an uncertainty of +/- 5%. There was no significant angular variation in the ratio of the measured and calculated yields. The angular distributions of bremsstrahlung calculated using available analytical theories dropped off more quickly with angle than the measured distributions. The predictions of the theories would be improved by including target-scattered photons.

Aluminum↗