Reduction potential and thermodynamic parameters of adrenodoxin by the use of an anaerobic thin-layer electrode

An enzymatic system to remove dissolved O2 in solution was applied to an optically transparent thin-layer electrode cell. This combination enabled the easy establishment of anaerobic conditions for the spectroelectrochemical study of O2-sensitive oxidation--reduction enzymes. By the use of the anaerobic cell with a small volume of 80 microliter, the formal reduction potential (E0) of adrenodoxin was found to be -250 +/- 2 mV vs a normal hydrogen electrode at 25 degrees C in a solution containing 0.1 M K-phosphate (pH 7.4) and 0.1 M KCl. Temperature-dependent experiments (5-25 degrees C) yielded the following thermodynamic parameters for the electron-transfer reaction of adrenodoxin: enthalpy (delta H0), -13.6 +/- 0.7 kcal/mol; entropy (S0red-S0ox), -49.6 +/- 2.4 eu. The large negative entropy value is quite unique among iron-sulfur proteins and heme proteins, suggesting that the protein structure changes dramatically upon one-electron reduction.

The effect of pH on the formal reduction potential of adrenodoxin in the presence and absence of adrenodoxin reductase: the implication in the electron transfer mechanism

We have investigated the formal reduction potentials (E degrees') of adrenodoxin with and without adrenodoxin reductase in order to elucidate the mechanism of electron transfer from adrenodoxin reductase (a flavoprotein) to adrenodoxin (an iron-sulfur protein). It was found by our spectropotentiostatic method that adrenodoxin showed no variation of E degrees' at different pH's in the absence of adrenodoxin reductase. The average E degrees' was -252 +/- 2 mV in the pH range between 6.0 and 8.3. In the presence of adrenodoxin reductase, adrenodoxin exhibited, on the other hand, a pH dependence of E degrees' at pH higher than 7.2 with a slope of -59 mV per pH unit: Adrenodoxin molecule possesses one protonation site with a pKa of 7.2. Cyclic voltammograms of adrenodoxin additionally revealed that the reoxidation reaction of reduced adrenodoxin is very slow in the absence of adrenodoxin reductase, but that it is readily reoxidized in the presence of adrenodoxin reductase.

Synaptic membrane antigens: detection and characterization

Analysis of the antigenic components of synaptic membranes presents several problems caused by detergents required to solubilize the proteins. These problems involve detection of the reaction between antibodies and proteins in the detergent extract as well as characterization of the individual antigens after further purification. We found a satisfactory solution for analysis of rat synaptic membranes by using rocket immunoelectrophoresis with an intermediate gel containing 0.5% berol to sequester sodium dodecyl sulfate (SDS) and an antibody gel containing 0.1% berol to maintain the solubility of the proteins. With antiserum prepared against a highly purified synaptic membrane fraction, these conditions gave rocket heights proportional to protein concentration (for the major rocket) and showed no reactions with membrane extracts of liver, kidney and spleen. By separation on gradient slab gels containing SDS, 4 antigenic polypeptides were found in Berol extracts of synaptic membrane, having apparent molecular sizes of 56,000, 58,000, 62,000 and 66,000 daltons. The SDS extract of the berol insoluble residue contained 3 antigenic polypeptides (12,500; 15,000, 16,500 daltons). The combined use of gradient slab gel electrophoresis in SDS and rocket immunoelectrophoresis with an intermediate gel to remove SDS provides a sensitive and rapid method for definitive identification of individual antigenic components in detergent extracts of membrane and for further purification of these antigens.

Glial fibrillary acidic protein in ependymomas and other brain tumors. Distribution, diagnostic criteria, and relation to formation of processes

Glial fibrillary acidic protein (GFAP) was studied in ependymomas by the three-step immunoperoxidase method and compared to results in astrocytomas and normal tissues. An order of reactivity for GFAP is presented. Diagnostic criteria, based on GFAP content, are proposed. In ependymomas GFAP-positive cells give rise to only some of the tumor cells, usually those forming tubules and perivascular arrangements. It is hypothesized that the same GFAP-positive cells may form tubules at their luminal poles and may produce perivascular arrangements at their other poles. The aberrant regulation associated with neoplastic transformation in glia is often, but not always, reflected in increased GFAP content. In both astrocytes and ependymal cells GFAP may have a similar function since in both cells the increase in GFAP appears to be related to the development of fibrillary processes.