Solubilization and separation of delta5,3beta-hydroxysteroid dehydrogenase and 3-oxosteroid-delta4-delta5-isomerase from bovine adrenal cortex microsomes

A physical separation of delta5,3beta-hydroxysteroid dehydrogenase and 3-oxosteroid delta4-delta5-isomerase solubilized from bovine adrenocortical microsomes is described for the first time. The solubilization as well as the separation was carried out with a mixture of a detergent: a substituted betaine (Empigen BB/P) and sodium cholate. This latter detergent protects isomerase from complete inactivation by Empigen and is necessary for the recovery of a significant amount of soluble isomerase. Separation of dehydrogenase and isomerase was successfully accomplished by the use of a DEAE-Biogel A anion-exchanger. Dehydrogenase activity was eluted, while the isomerase was retained. Measurements of dehydrogenase activity with androst-5-en-3beta-ol-17-one, pregnen-3beta-ol-20-one and pregn-5-en-(3beta,17alpha)-diol-20-one and of isomerase activity with androst-5-en-(3,17)-dione and pregn-5-en-(3,20)-dione suggested that more than one isomerase and more than one dehydrogenase form were present.

Investigation of two deoxygenated haemoglobin-haptoglobin complexes by Mössbauer spectroscopy

Haemoglobin Haptoglobin complexes formed when [Hp+]/[Hb]= 1/1 and [Hp]/[Hb] =2/1 were investigated by 57Fe Mössbauer spectroscopy. Both samples gave a spectrum consisting of a single quadrupole doublet. The temperature dependence of the quadrupole splitting was also identical for both samples. This proves that in both samples the nearest neighbour environment of the iron atom must be the same. A comparison with earlier investigations on myoglobin and haemoglobin indicates that the electronic structure of iron in the HbHp-complexes is similar to that in myoglobin.

Lipid requirement of membrane-bound 3-oxosteroid delta4-delta5-isomerase. Studies on beef adrenocortical microsomes

The role of phospholipid in the beef adrenal microsomal 3-oxosteroid delta4-delta5-isomerase (EC 5.3.1.1) has been investigated with the use of phospholipase A to alter the microsomal phospholipids. The byproducts of phospholipase A digestion have been removed with a wash solution containing bovine serum albumin. Removal of 80-85% of the phospholipid leads to loss of 80-90% of the 3-oxosteroid delta4-delta5-isomerase activity. Reconstitution experiments have been performed by introduction of lipid aqueous dispersions in the enzymatic assay. Asolectin, a commercially available preparation of soy phosphatides, is able to stimulate the enzymatic activity but does not restore the 3-oxosteroid delta4-delta5-isomerase activity in phospholipase-A-treated membranes. In contrast, the introduction of aqueous dispersions of microsomal total lipid mixtures in the enzymatic assay brings about a complete restoration of the 3-oxosteroid delta4-delta5-isomerase activity in the lipid-depleted membranes. It is concluded that the bovine adrenal microsomal 3-oxosteroid delta4-delta5-isomerase requires phospholipid(s) to exhibit its full catalytic activity.

Binding of human hemoglobin and its polypeptide chains with haptoglobin coupled to an agarose matrix

The interactions of human haptoglobin covalently linked to agarose with human hemoglobin and with p-chloromercuribenzoic-acid-treated alpha and beta chains (alpha* and beta* chains) were studied by flow chromatography and equilibrium binding. The results indicate that in solid state, haptoglobin maintains the same binding characteristics as in solution, the order of binding affinities being: hemoglobin greater than alpha* chain greater than beta* chain. The study of the binding parameters of the alpha* chain shows an heterogeneity of binding sites on the haptoglobin and an average affinity constant Ka of 3.6 X 10(4)l/mol.

Haptoglobin--haemoglobin interaction. Heterogeneity of the haptoglobin 1-1 molecule in its binding affinity for horse R/E-hemoglobin

The formation of two different complexes when haptoglobin (Hp) and haemoglobin (Hb) are mixed in a 1:1 molar ratio is demonstrated by isoelectrofocusing. In these two complexes, the affinity of Hp for Hb is shown to be different, since Hb can be displaced only from one of the complexes, by a further addition of Hp. This is confirmed by a quantitative study of the reaction stoichiometry, when [Hp]/[Hb] = 1 and [Hp]/[Hb] greater than 1, which allows an evaluation of the amount of each complex formed. All these data cannot be explained other than by the existence of two forms of Hp molecule and a reaction scheme which fits these experiments is proposed.

A study of Folch-Pi apoprotein. II. Relation between polymerization state and conformation

A comparison of the conformation of Folch-Pi apoprotein in organic solvent and in aqueous solutions has been made by ESR, infrared and circular dichroism spectroscopy studies. Electrophoresis and ultracentrifugation have been carried out in order to correlate molecular weight and charge of the molecule with its conformation. It appears that the protein is monomeric in organic solution. In water, only one component is present but the molecules behave as a polydisperse system of associating molecules. Hydrophobic interacitons seem to be important for this polymerisation which does not appear to be accompanied by the formation of beta-structure. After the transfer of the protein from organic solution to water, the ESR spectra of the protein labelled on the free SH groups show an heterogeneity in the motional environment of the label which permits to assume that different areas of association exist in the polymeric molecule.

Study of the apoprotein of Folch-Pi bovine proteolipid. II. Characterization of the components isolated from sodium dodecyl sulfate solutions

Acrylamide gel electrophoresis in dodecyl sulfate solutions of Folch-Pi apoprotein shows several bands. The different components were separated by Biogel P-200 filtration and then reduced and carboxymethylated. A comparative study of the amino acid composition, N-terminal sequence and C-terminal amino acid of the different components led to the assumption that their primary sequences are similar. Evidence for a contamination of the protein by free amino acids might explain the difference in terminal groups found by us and by other groups. It has been shown that the purified components can polymerize independently of S-S bond formation or exchange. The polymerization products were found to resist dissociation by dodecyl sulfate. It has been suggested therefore that the differences in migration rates of the various components are related to their shape rather than to their molecular weight.

Thermal and solvent perturbation as probes of conformational heterogeneity of haptoglobin 1-1

The shifts which occur in the ultraviolet spectra of haptoglobin 1-1 (Hp) and a conformational isomer with lower affinity for hemoglobin (Hp), in response to temperature and solvent changes, have been measured by difference spectra. The thermal difference spectra provide evidence for a different participation of tryptophyl residues in the conformational stability of Hp and Hp. Solvent perturbations have allowed an estimation to be made of the number of surface chromophores in the native Hp and Hp. These results are compatible with the existence of two Hp conformational isomers with different free energy, separated by a high-potential barrier.

Mammalian 3-oxosteroid delta4-delta5-isomerase: a membrane-bound enzyme. I. Fluorescence study of the relationship between the enzymatic binding site, phospholipids, water and ions

The microsomal membranes and the proteolipidic particles obtained by disruption of the microsomes by alkaline-earth ions at molar concentration have been compared by measuring the fluorescence properties of 1-anilino-naphthalene-3-sulfonate and naphthyl-1-phenylamine. The protein lipid arrangement of these two systems appears to be not essentially different. The study of fluorescence polarization of an hydrophobic probe (perylene) in function of Mg2+ concentration suggests a possible mechanism of disruption of the membrane by Mg2+ involving the strong structure-making effect of the ion. The comparison of the fluorescence polarization changes of perylene and equilenine (a competitive inhibitor of the isomerase) with the ionic concentration indicates that there is no direct relation between the bulk lipidic phase and the enzymatic binding site properties. Moreover, the emission of equilenine is completely quenched by I-, in contrast with the napththyl-1-phenylamine and perylene probes, which clearly demonstrates the accessibility of the catalytic site to water molecules and ions.

Mammalian 3-oxosteroid delta4-delta5-isomerase. A membrane-bound enzyme. II. Activation by divalent cations

Alkaline-earth ions (Mg2+, Ca2+ and Sr2+) have two specific effects on the kinetic parameters of the beef adrenal 3-oxosteroid delta4-delta5-isomerase activity in the microsomes and in the particles obtained after disrupting the membrane structure by action of 1 M MgCl2. On the microsomal enzyme, a 2-fold increase of V is observed with the three cations under study. The small difference in the effect of the three ions could be related to their hydration energy. It is suggested that the interaction of the ion with water is the determinant step of the activation mechanism and not the fixation of the ion on the enzyme or on some others possible binding sites in this system. With the enzyme in the proteolipidic particles, the use of EDTA as a chelating agent for the cations present in the enzymatic assay, allows the characterization of two effects: at low concentration of EDTA, an increase of Km is observed and at higher concentration (2 mM), V is decreased. A subsequent addition of Mg2+ leads to an activation in two steps: V is increased in the first step without change in Km, the second step consists of a decrease of Km without any change in V. A relation between the structural perturbations induced by the ions (Gallay, J., Vincent, M. and Alfsen, A. (1975) Biochim. Biophys. Acta 397, 489-500) and their kinetic effect on the enzymatic reaction is established.

Kinetics of the reaction between oxygen and haemoglobin bound to haptoglobin

The kinetics of the reaction between O(2) and haemoglobin bound to haptoglobin 1-1 were investigated by the stopped-flow and temperature-jump techniques. The reaction, which follows second-order kinetics in the lower concentration range, becomes independent of O(2) concentration above about 150mum-O(2).

Sex steroid binding plasma protein (SBP)

The detection, preparation from plasma Cohn fraction IV and purification of SBP are reported. The association constant has the value of K = 1.2 and 0.5 109 M−1 at 4°C for testosterone and oestradiol, respectively. A preparation homogeneous by the criteria of polyacrylamide gel electrophoresis, binding studies and ultracentrifugation is obtained; sedimentation equilibrium experiments give a molecular weight of approx. 52 000, confirming the approximative value obtained from Sephadex filtration.