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M Marden

Publications and source records attributed to M Marden.

24 records · Page 2Linked to original sources
PubMed1983

Electro-optical measurements on aqueous suspension of purple membrane from Halobacterium halobium.

The permanent dipole moment, polarizability, and the retinal angle of Halobacterium halobium purple membranes were determined at different pH values. All of the parameters have a maximum between pH 5 and 6. There is a reversal in the direction of the permanent dipole moment near pH 5. The value of permanent dipole moment was determined to be 60 D/protein at pH 6.6, and the value obtained for polarizability was 3 X 10(-28) Fm2/membrane fragment. The retinal angle of all-trans retinal was 0.8 degrees smaller than that of the 13-cis conformation.

Bacteriorhodopsins↗
PubMed1978

Fast reactions in carbon monoxide binding to heme proteins.

Using fast flash photolysis, we have measured the binding of CO to carboxymethylated cytochrome c and to heme c octapeptide as a function of temperature (5 degrees-350 degreesK) over an extended time range (100 ns(-1) ks). Experiments used a microsecond dye laser (lambda = 540 nm), and a mode-locked frequency-doubled Nd-glass laser (lambda = 530 nm). At low temperatures (5 degrees-120 degreesK) the rebinding exhibits two components. The slower component (I) is nonexponential in time and has an optical spectrum corresponding to rebiding from an S = 2, CO-free deoxy state. The fast component (I*) is exponential in time with a lifetime shorter than 10 mus and an optical spectrum different from the slow component. In myoglobin and the separated alpha and beta chains of hemoglobin, only process I is visible. The optical absorption spectrum of I* and its time dependence suggest that it may correspond to recombination from an excited state in which the iron has not yet moved out of the heme plane. The temperature dependences of both processes have been measured. Both occur via quantum mechanical tunneling at the lowest temperatures and via over-the-barrier motion at higher temperatures.

Binding Sites↗
PubMedDate not supplied

Abnormal rheological response of erythrocytes caused by nitroimidazoles and hyperthermia.

The aim of the present study was to investigate the response of erythrocytes to hyperthermia in combined treatment with nitroimidazoles. The efficiency of nitroimidazoles and physical agents on the rheological response of erythrocytes was measured by the viscosimetric-diffractometric method in a continuous osmotic gradient with constant shear stress of 100 dyn/cm2. We found that three newly synthesized dinitro- or nitroimidazole derivatives caused oxidative damage of erythrocytes in aerobic conditions. Nitroimidazole structure-dependent decrease of erythrocyte deformability was accompanied by oxidation of haemoglobin and depletion of reduced glutathione, lipid peroxidation and alteration of membrane structure indicated by a decrease of the ANS fluorescence intensity and increased production of MDA. Heat treatment per se (from 42 to 45 degrees C) only slightly decreased the erythrocyte deformability, but markedly enhanced the structure-dependent effect of nitroimidazoles. Erythrocytes heated at 45 degrees C with dinitroimidazole derivative III lost their deformability without haemolysis. Dithiothreitol used in combination with nitroimidazoles during a heating period to 43.5 degrees C protected cell deformability entirely, indicating an important role for disulphide bond formation in membrane proteins submitted to oxidative stress and hyperthermia.

Dithiothreitol↗