Search PubMed⌕ Search

Biomedical subjects

D King

Publications and source records attributed to D King.

At least 271 records · Page 15Linked to original sources
PubMed1979

Inactivation of Hydrogenase in Cell-free Extracts and Whole Cells of Chlamydomonas reinhardi by Oxygen.

O(2) irreversibly inactivates hydrogenase from Chlamydomonas reinhardi. The mechanism for the inactivation involves the reaction of one molecule of hydrogenase with one molecule of O(2) (or two oxygen atoms) in the transition complex of the rate-limiting step. The second order rate constant for this reaction is 190 atmospheres(-1) minute(-1) (1.4 x 10(5) molar(-1) minute(-1)). At levels above 0.01 atmosphere O(2), the increased numbers of O(2) molecules may compete for the site of inactivation hindering the proper orientation for inactivation of any one O(2) molecule and resulting in lowered rates of inactivation.CO is a reversible inhibitor of hydrogenase acting competitively against H(2). The K(i) for CO is 0.0010 atmosphere. CO antagonizes O(2) inactivation. In a period when complete inactivation by O(2) would usually occur, the presence of CO greatly reduces the inactivation rate.After 3 hours of adaptation in whole cells, the presence of H(2) lowers the rate of deadaptation of hydrogenase. Inasmuch as H(2) promotes increased O(2) uptake the cellular concentration of O(2) is likely to be lower. After 48 hours of adaptation O(2) uptake is reduced even when H(2) is present and the pattern of deadaptation under O(2) with and without H(2) and CO is qualitatively the same as observed for the inactivation of cell-free hydrogenase. The mechanism of inactivation of cell-free hydrogenase by O(2) may be the same as the mechanism for loss of hydrogenase during deadaptation in whole algal cells.

Journal Article↗
PubMed1978

The theory of tree bole and branch form.

Working from the general postulate that natural selection of plant form operates so as to maximize the survival potential of a species, this paper examines the hypothesis that the mechanical support of tree foliage must approach optimality in the use of wood, i.e., that tree stems and branches will have "optimal form" with respect to the amount of support tissue. Mathematical models of bole and branch form are presented, based on the proposition that either wind or gravity are the primary limiting factors for tree size and shape. Predictions of trunk and branch diameter as a function of tree size were tested with dimensional measurements of Populus tremuloides. The individual stems were selected from close-grown stands of differing ages. For small and intermediate trees, trunk diameter is such that stems have only 1.6 times as much wood as the minimum required to keep the tree from buckling under its own weight due to elastic instability. Branch diameters are shown to be close to the minimum required to maintain the spatial position of growing branches, as well as withstand wind forces. This minimal branch cost not only reduces the load which the stem must support against elastic instability, but allows the crown to flex in high winds. The flexing, in turn, reduces the drag force exerted by the wind on the trunk. Thus, the hypothesis that the observed tree form is an optimal design cannot be rejected on the basis of these results. Additional studies are planned with respect to optimal foliage distribution.

Ecology↗
PubMed1978

Steroid priming of the luteinizing hormone response to luteinizing hormone releasing hormone.

Perifusion experiments were performed to study the stimulatory effects of luteinizing hormone releasing hormone (LH-RH) on the release of LH from anterior pituitary tissue. Exposure of pituitary tissue from normal male rats to LH-RH (5 ng/ml for 5 min) induced a small release of LH; in tissue from ovariectomized rats receiving no pretreatment, the release was more than three times greater and in tissue from gonadectomized male or female rats pretreated with oestradiol benzoate and progesterone, the release was six times greater than that observed in normal rats. Further exposure of pituitary tissue from gonadectomized steroid-pretreated male and female rats to LH-RH (5 ng/ml) induced an increase in the level of LH even greater than that seen after the initial exposure (priming action of LH-RH); in tissue from ovariectomized rats receiving no pretreatment, less LH was released than after the first exposure to LH-RH and in tissue from normal male rats the response was unchanged.

Animals↗
PubMed1977

The adverse effects of elemental diets on tolerance for 5-FU toxicity in the rat.

The effects of a group of elemental diets on the gastrointestinal toxicity of 5-FU in the Sprague-Dawley rat were evaluated. Diarrhea, stomatitis, hypoalbuminemia, and early deaths were more frequent in the animals on elemental diets than in those consuming standard rat chow. Sepsis and hypoalbuminemia were directly related to the extent of protein hydrolysis of the particular elemental diet.

Amino Acids, Essential↗
PubMed1977

Pathological and therapeutic consequences of sleep loss: a review.

Until recently sleep deprivation has been studied from the point of view of determining whether or not it produces deleterious effects. Evidence, however, has begun to accumulate indicating that both REM deprivation and single night sleep deprivation may have antidepressant effects. Although beneficial effects are found primarily in endogenously depressed patients, variable results have been obtained in both "endogenous" and "reactive" depressions, suggesting that these diagnostic categories include biologically heterogeneous populations.

Adjustment Disorders↗
PubMed1976

Traumatic dislocation of the hip joint in children.

Between 1949 and 1972, 24 children under the age of 16 years were admitted to Middlemore Hospital with traumatic dislocation of a hip. Half of these were between 12 and 15 years of age, and there was a predominance of boys in the ratio of 7:1. A survey of these children supports the view that the hip joint of a child becomes dislocated more readily than that of an adult.

Adolescent↗
PubMed1976

Conduction velocity in the proximal segments of a motor nerve in the Guillain-Barré syndrome.

Conduction velocity from spinal cord to axilla (estimated using the F wave) has been compared with conduction velocity from axilla to wrist (measured in the conventional manner) in the motor fibres of the ulnar nerve in 17 controls subjects and in 11 patients with the Guillain-Barré syndrome (GBS). In the patients with GBS the conduction velocity was, in general reduced to a similar extent in both the proximal and the distal portions of the motor fibres, suggesting that the disease process is usually diffuse. In two patients, however, the conduction velocity in the proximal segment was disproportionally reduced and in one of these the conduction velocity in the distal segment was normal. It is concluded that the estimation of conduction velocity in the proximal segments of motor nerves may be of value in the assessment of patients with GBS.

Adolescent↗
PubMed1976

Season of birth in schizophrenia: an Australian study.

The authors have studied the season of birth in schizophrenics comparing those born in both southern and northern hemispheres. Their findings do not support the notion of seasonal variations claimed by other authors. The clinical significance of reports published in the literature is questioned.

Adolescent↗
PubMed1975

Dumbbell neuroblastomas in children.

A "dumbbell" neuroblastoma is a malignant neoplasm usually primary in the mediastinum or retroperitoneum with posterior extension through an intervertebral foramen to additional tumor within the spinal canal. Neurologic deficits are found in almost all cases. Nineteen patients with such tumors were reviewed with respect to diagnosis, management, and results. Treatment consisted of prompt laminectomy with total or subtotal excision of the extradural tumor. The primary tumor in the mediastinum or retroperitoneal area was removed at a second stage. All patients received postoperative radiation therapy. Eleven of the 17 patients observed more than two years are free of disease, a cure rate much higher than the overall experience with neuroblastoma. Substantial recovery of neurologic function occurred in most, but kyphoscoliotic deformities were a disturbingly frequent late complication.

Abdominal Neoplasms↗
PubMed1975

Lung biopsy in immunocompromised hosts.

Ninety-five lung biopsy procedures in 78 immunocompromised patients yielded treatable diagnoses in 35 per cent of the needle aspirates, 46 per cent of the cutting needle biopsies and 65 per cent of the open thoracotomies. Complication rates of bleeding or pneumothorax were comparable to those previously described in nonimmunocompromised patients. In patients with coagulation defects, the risk of having bleeding complications was high. Among 44 patients with primary lymphoma, 22 (50 per cent) had a lymphomatous infiltrate in the lung. Twenty-two patients with severe hypoxemia were studied and their mortality, although significantly greater than in the patients without hypoxemia, was marginally improved when a treatable lung lesion was found. The over-all recovery rate was 70 per cent when a treatable diagnosis was made in contrast to 25 per cent when there was no specific diagnosis. Hence lung biopsy, particularly by thoracotomy, appears to be a valuable procedure in immunocompromised patients who have otherwise undiagnosable lung lesions.

Adolescent↗