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Biomedical subjects

A Ulrich

Publications and source records attributed to A Ulrich.

At least 73 records · Page 4Linked to original sources
PubMed1987

A mutant insulin receptor with defective tyrosine kinase displays no biologic activity and does not undergo endocytosis.

The cDNAs encoding the normal human insulin receptor (HIRc) and a receptor that had lysine residue 1018 replaced by alanine (A/K1018) were used to transfect Rat 1 fibroblasts. Lysine 1018 is a critical residue in the ATP binding site of the tyrosine kinase domain in the receptor beta-subunit. Untransfected Rat 1 cells express 1700 endogenous insulin receptors. Expressed HIRc receptors had levels of insulin-stimulable autophosphorylation in vitro comparable to normal receptors, whereas A/K1018 receptors had less than 1% of that activity. Stimulation by insulin of HIRc receptors in situ in intact cells led to phosphorylation of beta-subunit tyrosine residues and activation of tyrosine kinase activity that could be preserved and assayed in vitro after receptor purification. In contrast, A/K1018 receptors showed no such activation, either of autophosphorylation or of kinase activity toward histone. Cells expressing HIRc receptors display enhanced sensitivity to insulin of 2-deoxyglucose transport and glycogen synthase activity. This increased sensitivity was proportional to insulin receptor number at low but not at high levels of receptor expression. A/K1018 receptors were unable to mediate these biologic effects and actually inhibited insulin's ability to stimulate glucose transport and glycogen synthase through the endogenous Rat 1 receptors. Expressed HIRc receptors mediated insulin internalization and degradation, whereas A/K1018 receptors mediated little, if any. Endocytotic uptake of the expressed A/K1018 insulin receptors was also markedly depressed compared to normal receptors. Unlike HIRc receptors, A/K1018 receptors also fail to undergo down-regulation after long (24 h) exposures to high (170 nM) concentrations of insulin. We conclude the following. 1) Normal human insulin receptors expressed in Rat 1 fibroblasts display active tyrosine-specific kinase, normal intracellular itinerary after endocytosis, and normal coupling to insulin's biologic effects. 2) A receptor mutated to alter the ATP binding site in the tyrosine kinase domain had little if any tyrosine kinase activity. 3) This loss of kinase activity was accompanied by a nearly complete lack of both endocytosis and biologic activity.

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PubMed1974

Effects of magnesium deficiency on the photosynthesis and respiration of leaves of sugar beet.

The effects of Mg deficiency on the photosynthesis and respiration of sugar beets (Beta vulgaris L. cv. F58-554H1) were studied by withholding Mg from the culture solution and by following changes in CO(2) and water vapor exchange of attached leaves. Leaf blade Mg concentration decreased from about 1200 to less than 200 meq kg(-1) dry matter without change in the rate of photosynthetic CO(2) uptake per unit leaf area, while from 200 to 50 meq kg(-1) the rate decreased to one-third. Rates of photorespiratory evolution of CO(2) into CO(2)-free air responded to Mg like those of photosynthetic CO(2) uptake, the rates decreasing to one-half, below 200 meq kg(-1). Respiratory CO(2) evolution in the dark increased almost 2-fold in low Mg leaves. Magnesium deficiency had less effect on leaf (mainly stomatal) diffusion resistance (r(1)) than on mesophyll resistance (r(m)); in Mg-deficient plants r(m) increased from 2.9 to 7.1 sec cm(-1), whereas r(1) became significantly greater than the control value only in the most severe instances of Mg deficiency.

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PubMed1973

Effects of phosphorus deficiency on the photosynthesis and respiration of leaves of sugar beet.

Phosphorus deficiency was induced in sugar beet plants (Beta vulgaris L. var. F5855441), cultured hydroponically under standardized environmental conditions, by removal of phosphorus from the nutrient supply at the ten leaf stage 28 days after germination. CO(2) and water vapor exchange rates of individual attached leaves were determined at intervals after P cutoff. Leaves grown with an adequate nutrient supply attained net rates of photosynthetic CO(2) fixation of 125 ng CO(2) cm(-2) sec(-1) at saturating irradiance, 25 C, and an ambient CO(2) concentration of about 250 mul l(-1). After P cutoff, leaf phosphorus concentrations decreased as did net rates of photosynthetic CO(2) uptake, photorespiratory evolution of CO(2) into CO(2)-free air, and dark respiration, so that 30 days after cutoff these rates were about one-third of the control rates. The decrease in photosynthetic rates during the first 15 days after cutoff was associated with increased mesophyll resistance (r(m)) which increased from 2.4 to 4.9 sec cm(-1), while from 15 to 30 days there was an increase in leaf (mainly stomatal) diffusion resistance (r(l)') from 0.3 to 0.9 sec cm(-1), as well as further increases in r(m) to 8.5 sec cm(-1). Leaf diffusion resistance (r(l)') was increased greatly by low P at low but not at high irradiance, r(l)' for plants at low P reaching values as high as 9 sec cm(-1).

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PubMed1973

Effects of potassium deficiency on the photosynthesis and respiration of leaves of sugar beet.

Sugar beet plants (Beta vulgaris L. var. F5855441) were germinated and cultured under standardized environmental conditions for 28 days. Potassium deficiency was then induced by withholding K from the culture solution. Changes in CO(2) and water vapor exchange rates and surface temperatures of individual attached leaves were measured with time after K cut-off, along with changes in the concentrations of the leaf minerals K, Na, Ca, Mg, Fe, Mn, Cu, and Zn. During the 1st week after K cut-off the concentration of Na in the leaf blade increased from 200 to 1000 milliequivalents per kilogram dry matter while K decreased from 1500 to 300 milliequivalents per kilogram. During the subsequent 2 weeks, both Na and K concentrations decreased. The concentrations of other leaf minerals, except Mn, were little affected by K cut-off. Photosynthetic CO(2) uptake per unit area decreased linearly with time after cut-off and attained one-third of the control rate after 21 days. Low K apparently decreased photosynthesis through an increase in mesophyll resistance to CO(2) (r(m)) from 2.8 to 5.3 seconds per centimeter in 21 days. Leaf (mainly stomatal) diffusion resistance (r'(1)) increased only slowly during the first 15 days from 0.3 to 0.5 second per centimeter, eventually reaching 1.6 seconds per centimeter at 21 days. Low K progressively decreased the photorespiratory evolution of CO(2) into CO(2)-free air, but steadily increased the rate of CO(2) evolution in dark.

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PubMed1973

Effects of Potassium Deficiency on the Photosynthesis and Respiration of Leaves of Sugar Beet under Conditions of Low Sodium Supply.

Sugar beet plants (Beta vulgaris L. cv. F58-554H1) were germinated and cultured under standardized environmental conditions. The effects of K deficiency on photosynthetic and respiratory CO(2) exchange rates of attached leaves were studied under conditions of low Na supply by withholding both Na and K from the culture medium at cut-off (28 days after planting). Potassium and Na concentrations in the leaf blade and petiole decreased rapidly during the 8 days after cut-off, then more slowly.Photosynthetic CO(2) uptake per unit leaf area decreased rapidly with time after cut-off to 23% of the control rate in 17 days. Mesophyll resistance to CO(2) (r(m)) increased sharply after cut-off, r(m) eventually attaining 8.3 sec cm(-1). Leaf (mainly stomatal) diffusion resistance, r(1)', also increased rapidly from 4 days after cut-off, reaching 1.9 sec cm(-1) 13 days later. The photorespiratory evolution of CO(2) into CO(2)-free air decreased progressively after cut-off, but the rate of dark respiratory CO(2) evolution increased. It was concluded that withholding Na as well as K at cut-off increased the deleterious effects of K deficiency on photosynthesis and stomatal opening.

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PubMed1972

Potassium Deficiency-induced Changes in Stomatal Behavior, Leaf Water Potentials, and Root System Permeability in Beta vulgaris L.

Studies of the water relations of potassium deficient sugarbeet plants (Beta vulgaris L.) revealed two factors for stomatal closure. One component of stomatal closure was reversible by floating leaf discs on distilled water to relieve the water deficit in the leaves; the other component was reversible in the light by floating the leaf discs on KCl solution for 1 hour or more. Potassium-activated stomatal opening in the light was observed when the guard cells were surrounded by their normal environment of epidermal and mesophyll cells, just as observed by previous workers for epidermal strips. Leaf water potentials, like stomatal apertures, appear to be strongly related to leaf potassium concentration. Potassium-deficient plants have a greatly decreased root permeability to water, and the implications of this effect on stomatal aperture and leaf water potential are discussed. In contrast, petiole permeability to water is unaffected by potassium treatment.

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PubMed1971

Interaction of rubidium or sodium with potassium in absorption by intact sugar beet plants.

This study concerns the selective absorption of K and Rb or of K and Na by intact sugar beet (Beta vulgaris) plants from modified conventional nutrient solutions over an extended period of plant growth. Long term results agreed with those of short term experiments by other investigators using excised root systems and simple salt solutions. Potassium and Rb were mutually competitive in their absorption. High selectivity of K relative to Na absorption was observed. Sodium was excluded during the early growth period of sugar beets.

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PubMed1971

Sodium absorption by intact sugar beet plants.

Sodium absorption by intact sugar beet plants (Beta vulgaris) was found to be mediated by at least two distinct mechanisms when uptake was studied over a wide range of Na and K concentrations. The first mechanism operates at low Na concentrations (<1 milliequivalent per liter); presence of K completely blocks this mechanism for Na. The second mechanism operates at high Na concentrations (>1 milliequivalent per liter), transporting Na as well as K; but apparently this mechanism is not active for Na absorption in young sugar beet plants up to the 10-leaf stage.

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PubMed1970

Interactions of rubidium, sodium, and potassium on the nutrition of sugar beet plants.

The effect of Rb on the growth and the development of sugar beet plants (Beta vulgaris, var. MS NB1 x NB4) depends on the Rb concentration, the K supply, and the relative abundance of Na. Rubidium added either to a low or high K solution with or without added Na increased leaf blade size greatly, possibly through an effect on phytohormones or through a "partitioning effect" on the distribution of carbohydrates, with top growth favored over storage roots.Sodium increased the growth of sugar beet plants when they were either K-deficient or adequately supplied with K. Sodium or Rb added to a high K solution increased the sucrose percentage and total sucrose of the storage roots significantly. Sodium and Rb supplied simultaneously to the nutrient solution resulted in synergetic effects only at low K supply.Potassium was translocated in mature leaves from the petiole to the blade when Na was added to a low K solution, or when Rb was added either to a low or a high K solution. Rb + K had little to no effect on Na redistribution.

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PubMed1967

Sodium and rubidium as possible nutrients for sugar beet plants.

This study concerned the degree to which Na or Rb could substitute for K in the growth of sugar beet plants when K in the culture solution was low (1 meq/liter) or high (12 meq/liter).Sodium at high concentrations increased the growth of plants in a basal nutrient medium when either deficient in K or when adequately supplied with K alone. Redistribution of K from petioles to blades could not fully explain these results. Therefore, the essentiality of Na per se for growth of sugar beet plants may be inferred.Rubidium increased the growth of plants significantly when supplied in small doses to a nutrient medium deficient or adequately supplied with K. The amount of K added and the mode of Rb addition to solution cultures should be carefully considered when studying the effect of Rb on growth. High Rb concentrations were toxic, especially to the growth of fibrous roots.Sodium or Rb have been shown to enhance the growth of sugar beet plants under either low or high K conditions. Essentiality of either Na and/or Rb per se for growth of sugar beets may be inferred, but other criteria should be fulfilled also for conclusive proof.

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PubMedDate not supplied

Excretion into the culture medium of a Bacillus beta-glucanase after overproduction in Escherichia coli.

The beta-glucanase gene (bgl) from Bacillus amyloliquefaciens was expressed in E. coli CSH 55 under the control of the PR promoter of phage lambda that is repressed by the thermosensitive repressor C1857. Production of beta-glucanase was drastically stimulated by a temperature shift to 42 degrees C. This overexpression of the bgl gene (about 20% of the total cellular protein) led to an almost complete excretion of the otherwise periplasmic protein into the extracellular medium, beta-glucanase accounted for more than 50% of the extracellular proteins. Col E 1 related plasmid (pEG 1) are amplified in E. coli relA strains in response to an amino acid limitation leading to a 10-fold increase in the activity of plasmid encoded genes. In this work we intended to maximize the expression of the bgl gene by a concerted action of a plasmid amplification and temperature induction. Surprisingly we could not increase the beta-glucanase production above the level reached by plasmid amplification or temperature induction alone. The reasons for this unexpected result will be discussed. Under all conditions tested the expression of the bgl gene was much lower in the E. coli relA strain NF 162 than in E. coli CSH 55; the low beta-glucanase production was accompanied by a reduced excretion rate of the enzyme.

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