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Biomedical subjects

K Lemke

Publications and source records attributed to K Lemke.

At least 19 recordsLinked to original sources
PubMed1992

Bacterial lipopolysaccharide induces tyrosine phosphorylation and activation of mitogen-activated protein kinases in macrophages.

Bacterial lipopolysaccharide (LPS) is a potent activator of antibacterial responses by macrophages. Following LPS stimulation, the tyrosine phosphorylation of several proteins is rapidly increased in macrophages, and this event appears to mediate some responses to LPS. We now report that two of these tyrosine phosphoproteins of 41 and 44 kDa are isoforms of mitogen-activated protein (MAP) kinase. Each of these proteins was reactive with anti-MAP kinase antibodies and comigrated with MAP kinase activity in fractions eluted from a MonoQ anion-exchange column. Following LPS stimulation, column fractions containing the tyrosine phosphorylated forms of p41 and p44 exhibited increased MAP kinase activity. Inhibition of LPS-induced tyrosine phosphorylation of these proteins was accompanied by inhibition of MAP kinase activity. Additionally, induction of p41/p44 tyrosine phosphorylation and MAP kinase activity by LPS appeared to be independent of activation of protein kinase C, even though phorbol esters also induced these responses. These results demonstrate that LPS induces the tyrosine phosphorylation and activation of at least two MAP kinase isozymes. Since MAP kinases appear to modulate cellular processes in response to extracellular signals, these kinases may be important targets for LPS action in macrophages.

Amino Acid Sequence↗
PubMed1989

Glucose determination by differential pulse voltammetry with a platinum electrode.

Measurements with differential pulse voltammetry were carried out using an electrocatalytic glucose sensor based on a three-electrode system with a smooth platinum working electrode in a flow-through-type arrangement. The geometric area of the working electrode was 0.5 mm2. The influence of environmental conditions (temperature, pH, pCO2, pO2) was tested using an appropriate parameter set for differential pulse voltammetry (pulse height between -10 and -100 mV, pulse width 40 ms, scan rate 20 mV/s). Also, investigations were conducted in the presence of co-reactants such as urea and some amino acids. Finally, the electrode was tested in human serum. A sequence of anodic and cathodic pulses (duration 1 s; +1150 mV; -950 mV vs. Ag/AgCl) was used as a short rejuvenation cycle (duration 12 s). The signal mostly dependent on glucose was found in the low potential region around -750 mV vs. Ag/AgCl. The calibration curves were nonlinear above a glucose concentration of 12.5 mmol/l. In the linear range, the sensitivity of the electrode was approximately 60 nA/mmol/l for a pulse amplitude of -10 mV; it increased by one order of magnitude at a pulse height of -80 mV. The presence of amino acids caused a decrease of the sensor current to about 35%. Varying their concentration between 50% and 150% of their average physiological values was without any influence on the measuring signal. A variation of the urea concentration between 2 and 10 mmol/l had an effect of about 12% of the magnitude of the glucose dependent sensor current. We found linear relations between cell current, temperature, and pH, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Biosensing Techniques↗
PubMed1989

Mathematical simulation of an enzyme-based glucose sensor with pO2-basic sensor.

In the design of enzyme-based sensors, the measuring characteristics are mostly obtained by the trial-and-error method. An alternative is provided by mathematical simulation of the behaviour of the sensors. For this, a mathematical model was outlined which is described by two coubled inhomogeneous partial differential equations for each layer of the sandwich membrane structure and by a set of boundary conditions. This model was used to simulate the dependence of the measuring characteristics (calibration curves, response time) on the design parameters (geometry, transport properties of the membranes, enzyme activity) of the enzyme-based glucose sensor. The simulated and the measured calibration curves are in good correspondence. With decreasing pO2, a stoichiometric limitation appears, and the linear range of measurement is reduced. If catalase is coimmobilized with glucose oxidase, the oxygen consumption is halved and the measuring range is doubled. The influences of diffusion coefficients and of specific enzyme activities on the sensitivity and response time are simulated. The results are in good accordance with theoretical statements and experimental results. The limits of the model are determined by its convergence properties.

Biosensing Techniques↗
PubMed1986

A comprehensive package for DNA sequence analysis in FORTRAN IV for the PDP-11.

A computer package written in Fortran-IV for the PDP-11 minicomputer is described. The package's novel features are: software for voice-entry of sequence data; a less memory intensive algorithm for optimal sequence alignment; and programs that fit statistical models to nucleic acid and protein sequences.

Base Sequence↗
PubMed1985

In vivo comparison of different algorithms for the artificial beta-cell.

Using an extracorporeal artificial beta-cell in chronically diabetic dogs, the effects of four different mathematical models of glucose-controlled insulin dosage were compared: the Biostator algorithm (quadratic equation), Toronto algorithm (hyperbolic tangent function), Karlsburg algorithm (modified first-order derivative controller), and Ilmenau algorithm (second-order linear difference equation). The constants of all formulas implemented for the artificial beta-cell were obtained by regression analysis of paired blood glucose and plasma insulin data from normal control animals. Thus, they were biologically equivalent for all formulas. The patterns of blood glucose, insulin doses, and plasma insulin before, during, and after an intravenous glucose infusion test performed during the glucose-controlled insulin infusion showed no significant differences between the experimental groups subjected to the different algorithms. However, in no case were really normal blood glucose response curves restored by the artificial beta-cell. This might be due, first, to the fact that the algorithm parameters were not adapted to the actual individual insulin responsiveness, second, to the unphysiological peripheral venous route of insulin administration, and, third, to the lack of appropriate adaptation of the animals to normoglycemia.

Animals↗
PubMed1985

Development of catalytic platinum-binder electrodes for glucose determination.

Compact catalytic platinum-binder glucose sensors were developed, provided for the artificial beta-cell. These consist of three electrodes: the working electrode, a 0.5 mm diameter glass-sheathed platinum wire, covered with a mixture of platinum black and binder (PMMA, PVC) at the face, the reference electrode and the rejuvenating or counter electrode. Measurements were carried out either by a non-equilibrium method within the anodic range or by determination of the current at the anodically directed peak during the cathodic scan. In the first case a periodical switching between rejuvenating and measuring potential takes place and, in the second case, the whole voltammogram is cycled between +1.2 V and -1.2 V (vs. Ag/AgCl). For measurements in phosphate-buffered saline at 37 degrees C the calibration curves exhibit an approximately linear dependence up to a glucose concentration of 30 mM; the sensitivity amounts to 0.3 microA mM-1 and the response times t90% are between 6 and 10 min. A urea concentration of 2.5 mM causes a decrease of the non-equilibrium current of 11.5%-3.0%, and a mixture of amino acids causes a current rise of 11.4%-2.7% with increasing glucose concentration. During the cathodic scan the amino acids affect the peak current negligibly, and the influence of urea reaches saturation for concentrations higher than 6.7 mM. Preliminary in vivo measurements permit the conclusions that after appropriate pretreatment the catalytic glucose sensors can be used for short-time blood glucose monitoring.

Animals↗