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Biomedical subjects

C Wenzel

Publications and source records attributed to C Wenzel.

6 recordsLinked to original sources
PubMed1991

Crosslinking of Dam methyltransferase with S-adenosyl-methionine.

Highly purified DNA-adenine methyltransferase was irradiated in the presence of different concentrations of radiolabelled S-adenosyl-methionine (AdoMet) with a conventional Mineralight UV-lamp from several minutes up to 1 h while incubating in ice. Incorporation of radioactivity was monitored by electrophoresis of the crosslink between S-adenosyl-methionine and Dam methylase on SDS-polyacrylamide gels followed by fluorography. Crosslinking reached a maximum in presence of 10 microM S-adenosyl-methionine; it was inhibited in the presence of substances which competitively inhibit methylation of DNA by Dam methylase, like sinefungin or S-adenosyl-homocysteine, but not in the presence of non-inhibitors like ATP or S-isobutyl-adenosine. The crosslink obtained was resistant against a wide range of even drastic conditions commonly used in protein and peptide chemistry. Proteins, which do not bind S-adenosyl-methionine, as well as heat inactivated Dam methylase were not photolabelled. After limited proteolysis the radioactive label appeared only in certain of the peptides obtained. From Western blots carried out with polyclonal antibodies produced against a synthetic peptide corresponding in its sequence to amino acids 92-106 of the Dam methylase, the crosslinking of AdoMet could be tentatively mapped at a position after amino acid 106.

Binding, Competitive↗
PubMed1990

Volume calibration of various gasmeters using a modified Tissot spirometer.

Various methods for determinating energy expenditure by indirect calorimetry are used in laboratory and field studies such as the Douglas bag method, often used in combination with a wet gasmeter, the respirometer of Kofranyi and Michaelis (KM) and the Oxylog (OX). To calibrate the volume measurements of these pieces of apparatus a modified Tissot spirometer was built, consisting of an outer casing filled with water, a core and a bell. It was equipped with a solid counterbalance and with an additional roller chain, partly freely suspended on the side of the counterbalance. This construction allowed compensation for the varying buoyancies of the bell. The lift of the bell was measured by means of a vernier scale. From calculations of the geometric volume a revolution counter was adapted to record the moved volume in litres. By means of this spirometer volumes up to 200 l can be used for calibration at various physiological flow rates. Calibration procedures for KM, wet gasmeters and OX were developed. For OX a small inaccuracy up to 2.0% was observed within the flow range from 20 to 70 l.min-1. The inaccuracy increased at higher flow rates. Under defined calibration conditions the modified Tissot spirometer enabled repeated calibrations of different types of gasmeters.

Calibration↗
PubMed1990

A comparative study on different methods for the determination of energy expenditure.

In order to determine energy expenditure, the Douglas Bag technique (DB) and Kofranyi-Michaelis respirometers (KM) have been widely used under field conditions for several decades. Some years ago the Oxylog (OX) method was developed, measuring simultaneously the difference of partial oxygen pressure in inspired and expired air (PO2 diff.) by two polarographic oxygen sensors. In order to compare these three methods laboratory experiments (3 test subjects, 5 different bicycle ergometer work loads, 180 measurements per apparatus) were performed. Oxygen uptake (VO2) varied between about 0.9 to 3.0 l/min. The VO2 data obtained by the DB method, which were used as a reference, and those obtained by the KM method agreed fairly well. The recorded data of OX underestimated VO2 up to 21%, with the deviation increasing with work intensity. A sufficient accuracy of recorded VO2 was observed only up to moderate work intensity. OX data calculated from ventilation volume of inspired air per minute (VI) and PO2 diff., measured by OX, were always about 19% higher than those recorded by OX. This means that the calculated VO2 values of the OX corresponded fairly well with DB values at heavy work loads. The reason for the differences between recorded and calculated OX data is still unknown. Further research is urgently needed.

Adult↗
PubMed1988

Physical versus pharmacological counter-measures. Studies on febrile rabbits.

128 experiments were carried out on febrile rabbits at air temperatures of 8, 18, 24 and 30 degrees C in order to analyze the thermoregulatory effects and mechanisms of physical and/or pharmacological counter-measures. Fever was achieved by injection of 0.1 micrograms Salmonella typhi endotoxin (LPS)/kg into an ear vein. As the pharmacological counter-measure, injections of acetylsalicylic acid (ASA) into an ear vein were chosen. For the physical counter-measure, cooling thermodes (5 degrees C) were constructed for the abdominal skin, for the ear and for the rectum. ASA injections had no effect on the first fever maximum, even if applied 20 to 60 min before the LPS injection, but eliminated the second fever maximum. Of course, the additional hyperthermia observed at 30 degrees C ambient temperature could not be eliminated by the injections. On the other hand, cooling procedures can obviously not affect the pyrogen-induced temperature increase, but reduce the hyperthermic effect of a higher ambient temperature. Rectal cooling was more effective than ear or abdominal skin cooling. Abdominal cooling evoked an increase in metabolic heat production. Application of combined physical and pharmacological counter-measures achieved the strongest and quickest reduction of the second maximum, whereas the first maximum was not affected, as in all other experiments. The study emphasizes the necessity of taking into account the time course of the effector mechanisms in order to discriminate between hyperthermic and febrile components of temperature increase. In the initial phase cooling measures would evoke unwanted regulatory responses of the effectors, whereas during the second febrile maximum they would achieve a quicker reduction of core temperatures.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

The role of the actin status in platelet behaviour.

The status of platelet actin has been studied analytically by the DNase-I inhibition assay. Exposure of platelets to diamide, which oxidizes sulphydryl groups, results in an increase of filamentous actin. Neutralization of the effect of diamide by addition of 2-mercaptopropionylglycine (2-MPG) or washing out the excess of diamide is associated with a normalization of the cellular actin status. These findings strongly suggest that the redox state of platelets is somehow involved in the process of actin polymerization. Alterations of the redox state in metabolically altered platelets could therefore account for changes in the G- to F-actin equilibrium. In the thrombin-induced actin polymerization the redox state of the cell seems to be not involved, since 2-MPG preincubation of platelets (1.25 mM, 30 min) does not inhibit the filament assembly.

Actins↗