PubMed Health⌕ Search

Biomedical subjects

W Michalke

Publications and source records attributed to W Michalke.

10 recordsLinked to original sources
PubMed2001

Simulations on the number of entanglements of a polymer network using knot theory.

Polymer networks, created on the computer using the Bond-Fluctuation-Algorithm, offer the possibility to count the number of entanglements. We generated networks consisting of 5000 chains that were cross linked at their end groups via tetra-functional cross linkers. The analysis of the topology was performed by computing the Homfly polynomial of the entanglements offering a much more precise determination of the knot and entanglement type than the Gaussian linking number. It also allows us to determine the influence of Brunnian links. Results concerning the connection between the chain length and the number of entanglements are shown.

Journal Article↗
PubMed2001

Immunolocalization of plasma-membrane H+-ATPase and tonoplast-type pyrophosphatase in the plasma membrane of the sieve element-companion cell complex in the stem of Ricinus communis L.

Plasma-membrane-located primary pumps were investigated in the sieve element (SE)-companion cell complex in the transport phloem of 2-week-old stems of Ricinus communis L. and, for comparison, in stems of Cucurbita pepo L. and in the secondary phloem of Agrobacterium tumefaciens-induced crown galls as a typical sink tissue. The plasma-membrane (PM) H+-ATPase and the tonoplast-type pyrophosphatase (PPase) were immunolocalized by epifluorescence and confocal laser scanning microscopy (CLSM) upon single or double labeling with specific monoclonal and polyclonal antibodies. Quantitative fluorescence evaluation by CLSM revealed both pumps in one membrane, the sieve-element PM. Different PM H+-ATPase antibody clones, raised against the PM H+-ATPase of Zea mays coleoptiles, induced in mouse and produced in mouse hybridoma cells, discriminated between different phloem cell types. Clones 30D5C4 and 44B8A1 labeled sieve elements and clone 46E5B11D5 labeled companion cells, indicating the existence of different phloem PM H+-ATPase isoforms. The results are discussed in terms of energization of SE transporters for retrieval of leaking sucrose, K+ and amino acids, as one of the unknown roles of ATP found in SEs. The function of the PPase could be related to phloem sucrose metabolism in support of ATP-requiring processes.

Antibodies, Monoclonal↗
PubMed2001

Molecular and physiological characterisation of a 14-3-3 protein from lily pollen grains regulating the activity of the plasma membrane H+ ATPase during pollen grain germination and tube growth.

A 14-3-3 protein has been cloned and sequenced from a cDNA library constructed from mRNAs of mature pollen grains of Lilium longiflorum Thunb. Monoclonal antibodies (MUP 5 or MUP 15) highly specific against 14-3-3 proteins recognised a 30-kDa protein in the cytoplasmic fraction of many various lily tissues (leaves, bulbs, stems, anther filaments, pollen grains, stigmas) and in other plants (Arabidopsis seedlings, barley recombinant 14-3-3). In addition, 14-3-3 proteins were detected in a microsomal fraction isolated from pollen grains and tubes, and the amount of membrane-bound 14-3-3 proteins as well as the amount of the plasma membrane (PM) H+ ATPase increased during germination of pollen grains and tube growth. No change was observed in the cytoplasmic fraction. A further increase in the amount of 14-3-3 proteins in the microsomal fraction was observed when pollen grains were incubated in germination medium containing 1 microM fusicoccin (FC) whereas the number of 14-3-3s in the cytoplasmic fraction decreased. Fusicoccin also protected membrane-bound 14-3-3 proteins from dissociation after washing with the chaotropic salt KI. Furthermore, FC stimulated the PM H+ ATPase activity, the germination frequency and the growth rate of pollen tubes, thus indicating that a modulation of the PM H+ ATPase activity by interaction with 14-3-3 proteins may regulate germination and tube growth of lily pollen.

14-3-3 Proteins↗
PubMed1990

Ghosts of chromaffin granules accumulate biogenic amines according to a "pump and leak system" without contribution of carrier-mediated efflux.

Unidirectional inward transport into, accumulation by and loss of biogenic amines from ghosts of bovine chromaffin granules were studied to determine whether a carrier-mediated process contributes to the outward passage of amines across the granule membrane. In the presence of ATP-Mg2+, incubated ghosts (30 degrees C; pH 7.3) showed a reserpine-sensitive (IC50 2-5 nmol/l), unidirectional, inward transport of catecholamine (CA = 70% adrenaline/30% noradrenaline), 5-hydroxytryptamine (5-HT) and tyramine with different Km values (mumol/l: tyramine 2; 5-HT 5; CA 8) but with the same Vmax [20 nmol/(mg protein.min)] during the first 3 min of incubation. During longer incubation, the rate of unidirectional inward transport declined rapidly with time to about 30 to 40%, at which level it stayed nearly constant from 50 to 100 min of incubation. As the decline of unidirectional transport was independent of the amine accumulated in the ghosts, it is concluded that it reflects ageing of the membrane vesicles. During incubation for up to 100 min with CA, 5-HT or tyramine (10- to 30-fold Km) in the presence of ATP-Mg2+, the amine content of the ghosts increased, approaching a steady-state content (nmol amine/mg protein: CA 400-500, 5-HT 250, tyramine 60), which was negatively correlated with the lipid solubility of the amine (tyramine greater than 5-HT greater than CA), whereas the rate of approach to steady state (t1/2 in min: CA 20-30, 5-HT 7-10, tyramine less than 5) was positively correlated. Low concentrations of reserpine (greater than or equal to 25 nmol/l) caused net loss of amine from amine-loaded ghosts by inhibition of inward transport. However, reserpine did not reduce the fractional rate of loss (FRL) of CA-loaded ghosts induced by NH+4 or uncoupling agents. Accelerated exchange diffusion was not found to occur at the granule membrane, as addition of high concentrations of 5-HT or dopamine to CA-loaded ghosts did not result in a higher FRL of CA than did blockade of inward transport by reserpine. Analysis of steady-state kinetics revealed the following features of the granule transport. The approach to steady state (t1/2) was independent of the rate of inward transport. The steady-state amine content of ghosts approached a limiting value as the external concentration of the amine was increased; it was determined by the same kinetic constants (Km and the time-dependent Vmax) as found for the rate of carrier-mediated inward transport.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗
PubMed1977

A gradient of diffusible substance in a monolayer of cultured cells.

Monolayers of hypoxanthine phosphoribosyl transferase-deficient and their corresponding wildtype cells have been placed adjacent to each other with a newly described method. Autoradiographs from such preparation after incubation with 3H-hypoxanthine allow the direct visualization of gradients of incorporated radioactivity at the border between the two cell types. The gradients can be described by an exponential function, and the amount of radioactivity incorporated decreases to less than 1% at a distance of 1 mm from the wild-type cells. A possible mechanism to convert exponential gradients to linear ones over a certain concentration range is discussed.

Biological Transport↗