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Biomedical subjects

M Thom

Publications and source records attributed to M Thom.

At least 73 records · Page 4Linked to original sources
PubMed1991

[The tooth transplant in orthodontic treatment planning].

The analysis of all examined transplant cases combined treated with orthodontics shows a success rate of 76%. It must be underlined that the germ development at the time of the transplantation is of utmost importance. The best possible time proved to be at a root development of 2/3 to 3/4. Exact indication position, a careful atraumatic operation method and a short time of operation are also important factors of a successful transplantation. If all these preconditions are met, this method can be recommended.

Adolescent↗
PubMed1991

Sensitivity to angiotensin II of forearm resistance vessels in pregnancy.

Resistance vessel sensitivity to angiotensin II in vivo was studied in 13 primigravid normotensive women (16-24 weeks gestation), and in 10 non-pregnant control women. Angiotensin II was infused into the brachial artery at doses of 10, 100, 1,000 and 10,000 fmol min-1 and forearm blood flow measured by plethysmography. Reduction in forearm blood flow at all concentrations of angiotensin II was significantly greater in non-pregnant than in pregnant women. The dose-response relationships, plotted semi-logarithmically, were similar in shape in each group but sensitivity to angiotensin II was reduced in pregnant subjects compared with non-pregnant women. This is most simply explained by an effect of pregnancy on the sensitivity to angiotensin II of vascular smooth muscle in forearm resistance vessels.

Adult↗
PubMed1988

High Performance Liquid Chromatography-Based Reevaluation of Disaccharides Produced upon Incubation of Sugarcane Vacuoles with UDP-Glucose.

A reanalysis of products formed after short-term incubation of sugarcane (Saccharum spp. hybrid cv H50-7209) vacuole preparations with uridine diphosphate [(14)C]glucose was performed. The results indicated that the ethanol-soluble substance previously identified as sucrose did not elute with sucrose when subjected to high performance liquid chromatography but had the same retention time as a disaccharide tentatively identified as laminaribiose.

Journal Article↗
PubMed1987

UDP-Glucose-Dependent Sucrose Translocation in Tonoplast Vesicles from Stalk Tissue of Sugarcane.

Tonoplast vesicles isolated from stalk parenchyma tissue of sugarcane plants transport sucrose via a uridine diphosphate glucose (UDPGlc)-dependent group translocator. No sucrose transport via an ATP-dependent system could be detected. The products of UDPGlc uptake in the vesicles were sucrose and sucrose phosphate which, upon hydrolysis with alkaline phosphatase and invertase, showed that both hexose moieties are derived from UDPGlc.

Journal Article↗
PubMed1986

A group translocator for sucrose assimilation in tonoplast vesicles of sugarcane cells.

Existence of a group translocator for sucrose transfer into vacuoles of sugarcane (Saccharum sp.) cells has been further confirmed by the use of tonoplast vesicles isolated from intact vacuoles. The group translocator depends on external UDP-Glucose (Glc) and, via a series of enzymic reactions within the tonoplast, sucrose phosphate and sucrose are deposited inside the vesicles. Fructose-6-phosphate was not required for UDP-Glc uptake, nor was it taken up. None of the other sugar phosphates tested were taken up nor were the nucleotide sugars, UDP-Galactose and ADP-Glc. The uptake of UDP-Glc was concentration-dependent with a K(m) of 1.2 millimolar and a V(max) of 83.3 nanomoles per minute per milligram protein. The optimum pH for UDP-Glc uptake was 7.0. Uptake of UDP-Glc was inhibited by para-chloromercuribenzene-sulfonic acid, UDP, and GDP; carbonyl cyanide m-chlorophenylhydrazone inhibited to a lesser extent.

Journal Article↗
PubMed1985

Group translocation as a mechanism for sucrose transfer into vacuoles from sugarcane cells.

Isolated vacuoles from sugarcane cells took up uridine diphosphate glucose (UDP-Glc) from the surrounding medium at a rapid rate. After a 7-min incubation of vacuoles with UDP-[14C]Glc, sucrose and sucrose phosphate were identified in the vacuole extract. UDP-Glc in the incubation medium was converted to hexose phosphates, sucrose, and glucose, with very little UDP-Glc remaining. Fructose 6-phosphate was not required for UDP-Glc uptake nor was [(14)C]fructose 6-phosphate taken up even in the presence of UDP-Glc. Glucose 6-phosphate and glucose 1-phosphate also were not taken up into vacuoles. UDP-Glc uptake showed saturation kinetics with a K(m) of 0.7 mM and a V(max) of 11.1 nmol/min per 10(6) vacuoles. The optimum pH for UDP-Glc uptake was between 6.5 and 7.0. Uptake of UDP-Glc could be inhibited by p-chloromercuriphenylsulfonic acid, UDP, and GDP, and to a lesser extent by carbonyl cyanide m-chlorophenylhydrazone. The UDP-Glc binding site was specific for UDP-Glc; adenosine diphosphate glucose was not taken up, and guanosine diphosphate glucose did not compete with UDP-Glc for the binding site. The results suggest that sucrose transfer into vacuoles from sugarcane is via a group translocation mechanism, probably involving five tonoplast-bound enzymes.

Journal Article↗
PubMed1985

Electrogenic proton translocation by the ATPase of sugarcane vacuoles.

Existence of a proton-translocating ATPase on the tonoplast of higher plants has been further confirmed by use of two experimental systems: (a) intact isolated vacuoles from sugarcane cells and (b) vesicles prepared from the same source. Addition of MgATP to vacuoles polarized the tonoplast by 40 millivolts to a value of +20 millivolts, but a large preexisting pH gradient across the membrane restricted the pH change to 0.2 unit. In vesicle preparations, the tonoplast was polarized to +66 millivolts by the addition of MgATP and the intravesicular space was acidified by 1 pH unit to pH 5.5. Proton translocation equilibrium is controlled by the protonmotive potential difference, maximal at 125 millivolts for sugarcane cells. Energization of the tonoplast occurred at physiological concentrations of MgATP. Specificity of MgATP for proton translocation was indicated by a much smaller effect of MgADP and MgGDP on the electrochemical gradient, although these substrates were also hydrolyzed by tonoplast preparation.

Journal Article↗
PubMed1985

Evidence for a plasmalemma redox system in sugarcane.

A plasmalemma-bound NADH-dependent redox system has been identified in protoplasts isolated from cell suspensions of sugarcane. This system oxidized NADH as well as NADPH, increased O(2) consumption 3-fold, and increased the pH of the external medium while the cytoplasmic pH was decreased. In the presence of NADH, ferricyanide was rapidly reduced and the external medium was acidified. The uptake rates of K(+), 3-O-methylglucose, leucine, and arginine were all decreased in the presence of NADH.

Journal Article↗
PubMed1984

Role of the ATPase of sugar-cane vacuoles in energization of the tonoplast.

Vacuoles of sugar-cane suspension cells contained a tonoplast-bound ATPase which was exclusively located on the cytoplasmic side of the vacuole. Vanadate and diethylstilbestrol had little effect on the vacuolar ATPase. ATP was the optimum substrate for the tonoplast ATPase, but there was also evidence for tonoplast-bound GDP-hydrolyzing and GTP-hydrolyzing enzymes which can interfere with the ATPase assay. Other phosphate anhydrides and esters were not hydrolyzed. The addition of MgATP polarized the tonoplast from about 0 mV to an interior-positive value of about +20 mV; MgADP and MgGTP had much less effect; MgGDP and ATP (in the absence of magnesium) had no effect on the membrane potential. The polarization of the tonoplast was insensitive to valinomycin, nigericin, and inhibitors of plasmalemma ATPase, but was strongly reduced by the uncoupler carbonylcyanide m-chlorophenylhydrazone. These data are interpreted as evidence for the action of tonoplast-bound ATPase as a pump which translocates protons into the vacuoles. The activity of the ATPase was highly specific for MgATP2-; the other important ionic states of ATP:ATP4-, HATP3-, MgHATP-, and Mg2ATP neither stimulated nor inhibited. The same was true for Mg2+. Since the protons were not brought to the catalytic site by protonation of the substrate, the tonoplast-ATPase may pick up the proton for translocation from the cytoplasm. The saturation kinetics for MgATP2- hydrolysis were biphasic, the higher affinity ATPase with Km value of 0.7 mM seems to be the physiologically relevant activity.

Adenosine Triphosphatases↗
PubMed1982

Vacuoles from Sugarcane Suspension Cultures : I. ISOLATION AND PARTIAL CHARACTERIZATION.

Vacuoles were isolated from suspension cultures of sugarcane (Saccharum sp.) cells by centrifugation of protoplasts at high g force against a 12% (w/v) Ficoll solution. Distribution of marker enzymes and Concanavalin A binding showed an 11% contamination of the vacuole preparation by cytoplasmic components, mitochondria, and endoplasmic reticulum, and 18% contamination by plasma membrane. Acid phosphatase, carboxypeptidase, protease, peroxidase, and ribonuclease activities were enriched in isolated vacuoles. Carboxypeptidase was tonoplast-bound, whereas the other enzymes were soluble. Sucrose, reducing sugars, and free amino acids were measured in protoplasts and vacuoles during growth of cells in suspension culture. Sucrose and reducing sugar content of vacuoles increased as the culture aged, while free amino acids decreased sharply.

Journal Article↗
PubMed1982

Vacuoles from Sugarcane Suspension Cultures : II. CHARACTERIZATION OF SUGAR UPTAKE.

Vacuoles, isolated from sugarcane (Saccharum sp.) cells, took up 3-O methylglucose and sucrose and the evidence suggests specific transport systems for these sugars. There was no evidence of sugar efflux from preloaded vacuoles. Vacuoles in situ accumulated 3-O methylglucose, sucrose, glucose, and fructose, as shown by incubation of protoplasts with labeled sugar and subsequent analysis of vacuolar and cytoplasmic radio-activity. During the initial minutes of incubation, the amount and concentration of labeled sugar was higher in the cytoplasm than in the vacuole, but subsequently there was active uptake and accumulation into the vacuole. The rate of hexose transfer into the vacuole in situ approached that of hexose uptake by isolated vacuoles; however, the rate of sucrose uptake by isolated vacuoles was below the in situ rate. The site of sucrose synthesis was in the cytoplasm.

Journal Article↗
PubMed1982

Vacuoles from Sugarcane Suspension Cultures : III. PROTONMOTIVE POTENTIAL DIFFERENCE.

The electrochemical proton gradient across the tonoplast of isolated (Saccharum sp.) vacuoles and vacuoles in situ was measured. The isolated vacuoles show no significant protonmotive potential difference, the pH gradient of 0.8 (inside acid) was balanced by a membrane potential of about -80 mv (inside negative). From pH and uncoupler insensitivity and K(+) sensitivity, it was concluded that the experimentally caused K(+) gradient created the electric potential.Qualitatively different results were obtained on vacuoles in situ: the pH gradient is greater (1.3), the membrane potential positive inside. Uncoupler sensitivity is evidence for an enzyme system transducing protons inward as a cause for the considerable protonmotive force at the tonoplast in situ.

Journal Article↗
PubMed1981

Mechanism of uptake of L-arginine by sugar-cane cells.

Suspension cells of sugar cane were used as a model system for cells of higher plants to study the mechanism of L-arginine uptake. The uptake system is specific for the L-arginine molecule in the fully ionized state, i.e. delta-guanidino group and alpha-amino group positively charged and carboxyl group negatively charged. This was concluded because the Km value for uptake increased strongly for: (a) L-arginine analogues which lack the charged carboxyl group (L-arginine methyl ester, agmatin); (b) L-arginine analogues, which lack the charged alpha-amino group (L-arginine acid, gamma-guanidinobutyric acid); (c) L-arginine analogues, which lack the charged delta-guanidino group or gamma-guanidinoxy group (L-citrulline, L-canavanine at neutral and alkaline pH-values). The importance of the positive charge of the delta-guanidino group or gamma-guanidinoxy group was further documented by Km values for L-arginine and L-canavanine at different pH values. Only at pH values where the gamma-guanidinoxy group is protonated, was there an effective uptake of L-canavanine and effective competition of L-canavanine with L-arginine. The length of the L-arginine molecule was less important: slightly larger (L-homoarginine) or shorter analogues (L-lysine) were taken up rather well. A spatial rearrangement at the alpha-carbon (D-ariginine) was, however, not tolerated. The uptake of L-arginine proceeds by electrogenic uniport, there is no evidence for symport or antiport of another molecule (though L-canavanine uptake at neutral pH value causes a transient alkalinization of the suspension medium). Charge equilibration is brought about by efflux of protons and potassium ions.

Amino Acids↗