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Biomedical subjects

L W Lee

Publications and source records attributed to L W Lee.

At least 73 records · Page 4Linked to original sources
PubMed1985

Physiological characterization of adaptive clones in evolving populations of the yeast, Saccharomyces cerevisiae.

Populations of a diploid strain of S. cerevisiae were grown in glucose-limited continuous culture for more than 260 generations. A series of seven sequential adaptive changes were identified by monitoring the frequency of cycloheximide resistance in these populations. Samples were taken from the continuous cultures following each adaptive shift and characterized physiologically to determine (1) the range of phenotypes that can be selected in a precisely defined constant environment and (2) the order and predictability of the occurrence of the adaptive mutations in evolving populations. The clones were characterized with respect to the growth parameters, maximum growth rate, saturation coefficient and yield, as well as for changes in cell size and geometry and rate of glucose uptake. The maximum growth rates of the seven adaptive clones were very similar, but in contrast the saturation coefficients differed substantially. Surprisingly, not all clones showed reductions in the saturation coefficients, in comparison to the immediately preceding clones, as would be predicted from classical continuous culture kinetics. In addition, yield estimates first increased and then decreased for later isolated adaptive clones. In general, the results suggest epistatic interactions between the adaptive clones, consistent with earlier published results. The rate of glucose uptake, as measured by 14C-xylose uptake, increased dramatically after the selection and fixation of seven adaptive clones. Progressive decreases in cell volume and changes in cell geometry, resulting in increased surface area to volume ratios, were also observed in the adaptive clones, but these changes were not always seen in other haploid and diploid yeast populations evolving under the same conditions. Such changes may be easily explainable in terms of the characteristics of the glucose-limited environment. The significance of the results to the evolution of microorganisms under nutrient-limiting conditions is discussed.

Biological Transport↗
PubMed1979

Respiration and heart rate in exercising land crabs.

Land Crabs, Cardisoma guanhumi, were fitted with respiratory masks and E.C.G. electrodes and run for 10 or 20 min on a treadmill at speeds of 150 and 300 cm/min. Aerobic metabolism increased linearly with the speed of locomotion. The recovery period was characterized by a large oxygen debt. The primary respiratory adjustment to exercise was an increased ventilation volume; only a minor increase in oxygen extraction occurred. The respiratory exchange ratio increased during exercise and during recovery, presumably correlated with a metabolic acidosis. These results are similar to data collected for exercising vertebrates and the net cost of locomotion of crabs appears similar to quadrupeds. However, the heart rate in exercising crabs changed in an unexpected way: during moderate exercise no change was noted, but during heavy exercise a bradycardia developed. The reduction in rate resulted from an increase in interbeat interval and frequent pauses in the heart beat.

Animals↗
PubMed1979

Evolution of olfactory receptor in oriental fruit fly Dacus dorsalis.

Male oriental fruit flies (Dacus dorsalis) from colonies in Taiwan and Hawaii were evaluated for limit of response to various analogues of methyl eugenol. The results are interpreted in terms of the geometry and allosteric requirements of the antennal receptor that triggers the characteristic methyl eugenol reflex. This receptor has evolved for complementarity to all portions of the methyl eugenol molecule and responds only to ortho-substituted benzenes with adjacent oxygen atoms or isoelectronic equivalents. Substantial differences in responses of Taiwan and Hawaiian D. dorsalis suggest that perceptible evolution of the receptor protein has occurred during the past 50 years. A plausible scheme for the coevolution of dacini flies with plants containing phenylpropionoid essential oils is outlined.

Journal Article↗
PubMedDate not supplied

Dynamic implications of hip flexion contractures.

Hip flexion contractures are a common complication in disabled patients. However, no previous study has examined reduced hip motion during gait. This retrospective analysis evaluates the relationship between the degree of hip flexion contracture found on static testing and the degree found during gait and also assesses the strength of the association between hip flexion contractures and compensatory mechanisms such as anterior pelvic tilting, increased knee flexion, and decreased contralateral step length. Clinical and quantitative gait laboratory data were obtained from 41 consecutive patients with mostly neurologically based impairments who presented with bilateral hip flexion contractures on Thomas testing (82 limbs). Correlation studies demonstrated a relatively weak association between the degree of peak hip extension during gait and hip flexion contracture by Thomas testing (r = 0.41, P < 0.0001). Limited hip extension was most closely associated with anterior pelvic tilting (r = 0.60, P < 0.0001), whereas Thomas test measurements yielded a correlation with anterior pelvic tilt of only r = 0.36 (P < 0.001) and were insignificant predictor variables of anterior pelvic tilting in regression analysis. Thus, peak hip extension and anterior pelvic tilting assessed during gait were poorly associated with the static Thomas test measurements, and anterior pelvic tilt was most strongly correlated with reduced hip extension during gait compared with the other compensatory mechanisms.

Adolescent↗