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K Heremans

Publications and source records attributed to K Heremans.

46 records · Page 3Linked to original sources
PubMed1979

Pressure effects on lipid-protein interactions in (NA+ + K+)-ATPase.

The (Na+ + K+)-stimulated ATPase activity decreases with increasing pressure and a plot of the logarithm of the activity versus pressure shows a change in slope at a defined breakpoint pressure (Pb). The value of Pb increases linearly with increasing temperature. A dT/dP value of 27.7 +- 0.4 (S.D.) K/1000 atm is obtained. This is in very good agreement with the pressure shift for the melting transitions in phospholipids and aliphatic chains. This strongly indicates that an aliphatic chain melting process is involved in the breakpoint in the Arrhenius plot and pressure dependence of (Na+ + K+)-ATPase. The p-nitrophenyl phosphatase activity of this enzyme also decreases with pressure. In this case the plot of the logarithm of the activity versus pressure is linear without a break-point. The temperature dependence for (Na+ + K+)-ATPase was also studied in the presence of fluidizing drugs: desipramine and benzylalcohol. The presence of these drugs had no effect on the inflection point in the Arrhenius plot.

4-Nitrophenylphosphatase↗
PubMed1979

Heat activation of Phycomyces blakesleeanus spores: theromdynamics and effect of alcohols, furfural, and high pressure.

The thermodynamic parameters for the heat activation of the sporangiospores of Phycomyces blakesleeanus were determined. For the apparent activation enthalpy (DeltaH(#)) a value of 1,151 kJ/mol was found, whereas a value of 3,644 J./ degrees K.mol was calculated for the apparent activation entropy (DeltaS(#)). n-Alcohols (from methanol to octanol), phenethyl alcohol, and furfural lowered the activation temperature of P. blakesleeanus spores. The heat resistance of the spores was lowered concomitantly. The effect of the alcohols was a linear function of the concentration in the range that could be applied. When the log of the concentration needed to produce an equal shift of the activation temperature was plotted for each alochol against the log of the octanol/water partition coefficient, a straight line was obtained. The free energy of adsorption of the n-alcohols to their active sites was calculated to be -2,487 J/mol of CH(2) groups. Although still inconclusive, this points toward an involvement of protein in the activation process. The effect of phenethyl alcohol was similar to the effect of n-alcohols, but furfural produced a greater shift than would be expected from the value of its partition coefficient. When the heat activation of the spores was performed under high pressure, the activation temperature was raised by 2 to 4 degrees K/1,000 atm. However, with pressures higher than 1,000 atm (1.013 x 10(5) kPa) the activation temperature was lowered until the pressure became lethal (more than 2,500 atm). It is known that membrane phase transition temperatures are shifted upward by about 20 degrees K/1,000 atm and that protein conformational changes are shifted upward by 2 to 6 degrees K/1,000 atm. Consequently, heat activation of fungal spores seems to be triggered by a protein conformational change and not by a membrane phase transition. Activation volumes of -54.1 cm(3)/mol at 38 degrees C and -79.3 cm(2)/mol at 40 degrees C were found for the lowering effect of high pressure on the heat activation temperature.

Alcohols↗
PubMed1978

Effect of high pressure, detergents and phospholipase on the break in the Arrhenius plot of Azotobacter nitrogenase.

It is shown that lipids are responsible for the breaks in the Arrhenius plots of Azotobacter nitrogenase. The physical evidence is that temperature at which the break occurs increases with increasing pressure by 20 K/1000 atm. This is in agreement with the pressure dependence of the transition temperature of several synthetic phospholipids. We also find the same pressure dependence for the broad transitions observed in Escherichia coli phosphatidylethanolamine and in the membrane lipids from Azotobacter itself. Detergents and phospholipase remove the break. Reconstruction can be performed only with specific phospholipids.

Azotobacter↗