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Biomedical subjects

J C Thomas

Publications and source records attributed to J C Thomas.

At least 109 records · Page 6Linked to original sources
PubMed1984

Rotational dynamics of transfer ribonucleic acid: effect of ionic strength and concentration.

We have investigated the influence of ionic strength and nucleic acid concentration on the rotational Brownian motion of Escherichia coli tRNA1Val by studying the decay of the fluorescence polarization anisotropy (FPA) of intercalated ethidium on a nanosecond time scale. The rotational relaxation time tau R remains essentially constant as the ionic strength is varied from 2 to 100 mM at a tRNA concentration of 54 mg/mL. tau R also remains practically unchanged as the tRNA concentration is varied from 0.3 to 54 mg/mL at an ionic strength of 130 mM. Present hydrodynamic theories generally predict a more pronounced concentration dependence for rotational diffusion than we observe. This disagreement may result from a nonrandom distribution of the tRNA molecules in solution due to electrostatic interactions. By combining independent data from time-resolved nuclear Overhauser effect (NOE) cross-relaxation experiments and FPA experiments on the same tRNA, we are able to estimate the interproton spacing for the guanine N1-H and the uracil N3-H of the GU-50 base pair in E. coli tRNA1Val. This distance is 0.272 nm.

Escherichia coli↗
PubMed1984

Effect of Mg2+ on solution conformation of two different transfer ribonucleic acids.

We have investigated the effect of Mg2+ on the solution conformation of two different tRNAs by studying the decay of the fluorescence polarization anisotropy of intercalated ethidium on a nanosecond time scale. In the presence of endogenous Mg2+, yeast tRNAPhe and Escherichia coli tRNAVal1 exhibit similar behavior; i.e., the fluorescence from the intercalated ethidium decays biexponentially with lifetimes of approximately 25 and approximately 5 ns, and the fluorescence polarization anisotropy decays with a lifetime of approximately 25 ns. However, once Mg2+ is removed from the two tRNAs, their behavior is no longer similar. In the case of yeast tRNAPhe, it appears that titrating with Mg2+ restores the tRNA to the condition that it was in prior to the Mg2+ removal. This is not so for E. coli tRNAVal1, in which case titrating with Mg2+ results in a two-component anisotropy decay with lifetimes of approximately 25 and approximately 6 ns. Rudimentary calculations indicate that the 6-ns component does not result simply from a change in conformation of the tRNA. However, torsional motions in the tRNA facilitated by a torsion "joint" with a rigidity approximately 1/40 that of intact linear phi 29 DNA would yield a decay component on this time scale with about the right amplitude. We are thus left with the possibility that (after initially removing magnesium) titrating tRNAVal1 with Mg2+ leads to increased internal flexibility and a significant amplitude of a deformational relaxation mode. At any rate, there is no question that after removal of Mg2+ tRNAPhe and tRNAVal1 display quite different solution conformation behavior. These findings are in qualitative agreement with recent 500-MHz 1H NMR results from solutions of these two tRNAs.

Cations, Divalent↗
PubMed1983

Fluorescence depolarization and temperature dependence of the torsion elastic constant of linear phi 29 deoxyribonucleic acid.

The torsion elastic constant alpha of linear phi 29 DNA has been determined as a function of temperature from 10 to 78 degrees C by studying the decay of the fluorescence polarization anisotropy (FPA) of intercalated ethidium dye. The time-dependent FPA was measured by using a picosecond dye laser for excitation and time-correlated single photon counting detection. Over the region 10-74 degrees C, alpha was effectively constant within experimental error, varying from (3.5 +/- 0.4) X 10(-12) dyn cm at 10 degrees C to (3.7 +/- 0.3) X 10(-12) dyn cm at 74 degrees C. At 78 degrees C, which is just above the melting temperature Tm = 76 degrees C, alpha decreased to (3.3 +/- 0.3) X 10(-12) dyn cm, and at 90 degrees C, where the DNA is completely denatured, both the fluorescence lifetime and the decay time of the FPA are characteristic of unbound ethidium bromide. The weak temperature dependence of alpha implies that DNA torsional deformations do not occur primarily at sites of high enthalpy perturbed structures such as open base pairs.

DNA↗
PubMed1983

The effect on cost of medical care for patients treated with an automated clinical audit system.

An automated clinical medical record and audit system was developed to evaluate the effect of modifying physician behavior at the control points in the ambulatory care process and to determine if this change was reflected in patient care cost outcomes. This study compared clinical and cost results of patients in an experimental group, who had the automated record and audit system, to a control group, who had a traditional clinic record without chart audit. Physicians responded to the automated audit suggestions at a rate of 50.25 in the experimental group and 37.3 in the control group. No major differences were observed in clinical outcomes, with the exception of the number of days of hospitalizations and, consequently, the cost of hospitalizations. The experimental group cost for hospitalizations was one-third of the control group and accounted for a majority of the differences in the total annual cost for the two groups.

Ambulatory Care↗
PubMed1980

Torison dynamics and depolarization of fluorescence of linear macromolecules. II. Fluorescence polarization anisotropy measurements on a clean viral phi 29 DNA.

The decay of the fluorescence polarization anisotropy (FPA) of ethidium bromide bound to DNA has been studied over a range of time-spans from 18 ns to 120 ns with the aid of a picosecond dye laser. These FPA data have been fitted to three different functional forms: (1) the single-exponential-decay-plus-baseline employed by Wahl et al.; (2) the Initial Exponential Decay Zone formula of a recently developed rigid-rod and torsion spring model for the torsion dynamics of DNA; (3) the Intermediate Zone formula of that same model. At any fixed experimental time-span the formulas (2) and (3) provide slightly better fits than formula (1), but cannot be distinguished from each other by reduced chi-squared values alone, However, only the Intermediate Zone formula fits the data from all different time-spans with the same set of physical parameters The parameters determined for formulas (1) and (2) vary with the time-span of the experiment in a characteristic manner that can be rationalized in the event that the FPA actually follows the Intermediate Zone curve. The fact that the torsion dynamics for this DNA is well described by the Intermediate Zone formula discounts the possibility of distinct widely spaced torsion joints in such clean DNAs. We are able to provide the first reliable value for the torsional rigidity of DNA, C = 1.29 +/- 0.10 X 10(-19) dyne cm2 in 0.01 M NaCl at 25 degree C.

Coliphages↗
PubMed1979

A questionnaire assessment of age differences in retention of recent and remote events.

Age-related differences in memory for recently and remotely dated events have been evaluated through questionnaire assessment. Results from previous studies employing the technique differ in the analysis of retrieval of recent and remote events. In attempting to reconcile extant results from the literature, the following study employed a group of healthy males ranging in age from 26 to 69. The results showed: 1. The elderly exhibited no impairment of the ability to remember recent colloquial events. 2. The elderly's surprisingly accurate recall of remote events was not a product of selective and frequent rehearsal.

Adult↗
PubMed1978

Prazosin and clonidine for moderately severe hypertension.

In a single-blind comparative study of the cases of 30 moderately hypertensive patients, clonidine hydrochloride and prazosin hydrochloride had similar effectiveness in lowering blood pressure. Neither agent had significant effects on the renin-aldosterone axis. Addition of polythiazide to prazosin and chlorthalidone to clonidine notably increased the antihypertensive effect of both drugs. Serum cholesterol levels were observed to decrease when prazosin and clonidine were given and to rise when the diuretics were added to the regimen. The patients treated with clonidine were troubled by side effects, particularly drowsiness and dry mouth. Prazosin was better tolerated, with side effects tending to diminish with time. The "first-dose" effect was seen in two patients given prazosin, but it did not limit treatment. Both diuretics induced notable hypokalemia.

Adult↗
PubMed1978

Age-related differences in serial binary classification.

In a two-choice serial task, three groups of subjects with median ages of 37, 54, and 69 years pressed one response lever when the current signal was the same as its immediate predecessor in a sequence, and the other when it was not. Four classes of events-same signal/same response, same signal/different response, different signal/same response, different signal/different response-occurred equally often. The reaction times of subjects in the oldest group exceeded those of the two younger groups by a constant amount under all conditions; there was no evidence that stimulus or response repetition interacted with age. The data from all age groups support only the hypothesis that repeating a given signal is sufficient to produce the repetition effect in a choice reaction task.

Adult↗
PubMed1978

Age and familiarity in memory scanning.

Sixty-five healthy males (31 to 75 years old) memorized lists of six letters (familiar or unfamiliar organization). Letters were then presented singly, and subjects responded yes or no according to whether a given letter was in the memorized set. Subjects of all ages took longer to respond in the case of the unfamiliar list. This was disproportionately true for the oldest subjects, consistent with the idea that the age-related differences in the unfamiliar condition could not be wholly accounted for by psychomotor factors. The distributions of response latencies in the oldest groups had greater variance and skew.

Adult↗
PubMed1978

Retrieval time from different memory stores.

Two experiments were carried out to measure age-related differences in speed of error-free recall by normal adults. The major results were that: (a) the time taken to read a word aloud (retrieval from lexical memory) does not increase appreciably until subjects reach their 60s; (b) the time taken to recall a verbal item just attended to (retrieval from primary memory) increases steadily throughout the adult years, and most markedly between the sixth and seventh decades; and, (c) the time taken to recall recent verbal information outside the span of attention (retrieval from secondary memory) also increases as a function of chronological age, at a relatively rapid rate and most markedly between the fifth and sixth decades. The effects are independent of the number of stimulus-response alternatives.

Adult↗
PubMed1977

Maximal aerobic power in women cadets at the U.S. Air Force Academy.

A sample of 17 women cadets of the U.S. Air Force Academy's Class of 1980 was assessed to determine their maximal oxygen consumption and percent body fat. The sample was selected using the ponderal index to insure a stratified sample of body types. The Short Balke protocol was used to determine Vo2 max, and the Siri and the Keys and Brozek equations were used to find percent body fat. The Katch and McArdle equation was employed to determine body density. The average Vo2 max for the women cadets was 46.1 ml/kg/min (S.D. = 4.0). Correcting for altitude, this value compares quite favorably with other reported values. The 24.8% mean body fat places these subjects well within the normal range for college age females. The female cadets of the Class of 1980 appear to be above their contemporaries in civilian life in circulo-respiratory fitness.

Adipose Tissue↗
PubMed1977

Age-related differences in naming latency.

Older people seem to have difficulty learning new materials, perhaps because it takes them longer to retrieve relevant encoding information from memory. To assess the effects of age on speed of retrieval, 60 healthy males from 25 to 74 were shown pictures of common objects they were to name aloud as quickly as possible. The older subjects took longer to name the pictured objects. This difference was minimized with practice or when the name was cued, but did not interact with word frequency. The pattern of results for healthy older subjects was not similar to that found by Wingfield for brain-damaged subjects.

Adult↗
PubMed1976

Effects of age and frequency of stimulus repetitions on two-choice reaction time.

Binary choice-reaction times for 123 males, 25-79 years of age, were obtained in a sequence of discrete trials in which the proportion of occasions that the same stimulus was presented twice in succession varied from .25, .50, and .75 or from .75, .50, and .25 over successive thirds of the sequence. Stimulus alternations were responded to more rapidly than stimulus repetitions by subjects in all age groups, especially in trial blocks with .75 alterations. The absolute differences in mean reaction time to stimulus alterations and repetitions increased with age. The results are consistent with the hypothesis that reaction times are affected both by pre-existing expectations for stimulus alternations as well as expectations for stimulus alternations or repetitions developed during the course of the experiment. Mean response latency as well as between- and within-subject variability in performance increased with age. Analyses of frequency distributions of the reaction times indicated that the psychomotor component of reaction time increases with age while the decision-making component becomes more variable.

Adult↗