Effects of protein-protein and protein-lipid interactions on heme site conformation in the mitochondrial b cytochromes

Removal of lipid from detergent-solubilized succinate cytochrome c reductase by a mild method leads to a series of changes in the optical and EPR spectra of the b cytochromes. This culminates in a state that resembles purified b cytochromes from the same source and bisimidazole ferriheme model complexes. Reconstitution of the lipid-depleted complex with phospholipid restores the native spectra in a significant fraction of the complexes in the early stages of lipid depletion. Once the final state has been reached, however, reconstitution has so far been incapable of restoring described in this communication can be related to a model for integral membrane cytochromes.     

Effects of the calcium channel blocker diltiazem on the excitability of mouse oocytes

Effects of the organic Ca antagonist diltiazem on Ca channels were studied in ovulated and unfertilized oocytes of the mouse by using intracellular recording techniques. The resting potential was not affected by diltiazem. The threshold level of the Ca action potential shifted slightly toward positive voltages with diltiazem concentration, but the shift was not statistically significant. The overshoot and maximum rate of rise of the Ca action potential were inhibited by the drug in a dose-dependent manner, but higher amounts of diltiazem were necessary to cause similar blocking effects on Ca channels in mouse oocytes than in other differentiated cells. Increases of external concentration of Ca²⁺ antagonized the degree of diltiazem inhibition. However, the sequence of block of Ca²⁺, Sr²⁺, and Ba²⁺ currents was different for diltiazem vs Cd²⁺. It is suggested that diltiazem inhibition can not be explained by simple competitive scheme, ie, antagonism between diltiazem and permeant cations does not occur at the same binding site associated with the Ca channel in mouse oocytes.     

Spectral properties of a novel cytochrome P-450 of a Saccharomyces cerevisiae mutant SG1. A cytochrome P-450 species having a nitrogenous ligand trans to thiolate

An altered cytochrome P-450 (SG1 P-450) was partially purified from Saccharomyces cerevisiae mutant SG1 which is defective in lanosterol 14 alpha-demethylation. Oxidized SG1 P-450 showed a Soret peak at 422 nm and the alpha peak was lower than the beta peak. This spectrum was considerably different from those of known low-spin P-450s, indicating a unique ligand structure of SG1 P-450. The absorption spectrum of ferric SG1 P-450 was superimposable on that of the imidazole complex of ferric P-450, suggesting the presence of a nitrogenous ligand such as histidine of the apoprotein at the 6th coordination position. SG1 P-450 was immunochemically indistinguishable from cytochrome P-450 of S. cerevisiae catalyzing lanosterol 14 alpha-demethylation (P-45014DM) but had no lanosterol 14 alpha-demethylase activity.     

Photoaffinity labeling of the TF1-ATPase from the thermophilic bacterium PS3 with 3'-O-(4-benzoyl)benzoyl ADP

3'-O-(4-Benzoyl)benzoyl ADP (BzADP) was used as a photoaffinity label for covalent binding of adenine nucleotide analogs to the nucleotide binding site(s) of the thermophilic bacterium PS3 ATPase (TF1). As with the CF1-ATPase (Bar-Zvi, D. and Shavit, N. (1984) Biochim. Biophys. Acta 765, 340-356) noncovalently bound BzADP is a reversible inhibitor of the TF1-ATPase. BzADP changes the kinetics of ATP hydrolysis from noncooperative to cooperative in the same way as ADP does, but, in contrast to the effect on the CF1-ATPase, it has no effect on the Vmax. In the absence of Mg2+ 1 mol BzADP binds noncovalently to TF1, while with Mg2+ 3 mol are bound. Photoactivation of BzADP results in the covalent binding of the analog to the nucleotide binding site(s) on TF1 and correlates with the inactivation of the ATPase. Complete inactivation of the TF1-ATPase occurs after covalent binding of 2 mol BzADP/mol TF1. Photoinactivation of TF1 by BzADP is prevented if excess of either ADP or ATP is present during irradiation. Analysis by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate of the Bz[3H]ADP-labeled TF1-ATPase shows that all the radioactivity is incorporated into the beta subunit.     

Optimum conditions for ursodeoxycholic acid production from lithocholic acid by Fusarium equiseti M41.

Ursodeoxycholic acid dissolves cholesterol gallstones in humans. In the present study optimum conditions for ursodeoxycholic acid production by Fusarium equiseti M41 were studied. Resting mycelia of F. equiseti M41 showed maximum conversion at 28 degrees C, pH 8.0, and dissolved oxygen tension of higher than 60% saturation. Monovalent cations, such as Na+, K+, and Rb+, stimulated the conversion rate more than twofold. In the presence of 0.5 M KCl, the initial uptake rate and equilibrium concentration of lithocholic acid (substrate) were enhanced by 5.7- and 1.7-fold, respectively. We confirmed that enzyme activity catalyzing 7 beta-hydroxylation of lithocholic acid was induced by substrate lithocholic acid. The activity in the mycelium was controlled by dissolved oxygen tension during cultivation: with a dissolved oxygen tension of 15% and over, the activity peak appeared at 25 h of cultivation, whereas the peak was delayed to 34 and 50 h with 5 and 0% dissolved oxygen tension, respectively. After reaching the maximum, the 7 beta-hydroxylation activity in the mycelium declined rapidly at pH 7.0, but the decline was retarded by increasing the pH to 8.0. Several combinations of operations, such as pH shift (from pH 7 to 8), addition of 0.5 M KCl, and dissolved oxygen control, were applied to the production of ursodeoxycholic acid in a jar fermentor, and a much larger amount of ursodeoxycholic acid (1.2 g/liter) was produced within 96 h of cultivation.     

Mechanisms of suppressed cell-mediated immunity and impaired antigen-induced interleukin 2 production in granuloma-bearing mice

Pulmonary granulomas were induced in BALB/c mice immunized with methylated bovine serum albumin in complete Freund's adjuvant by the intratracheal injection of plain agarose beads or beads conjugated to specific antigen. Large hypersensitivity granulomas developed around antigen-coupled beads in immunized animals. Smaller but still prominent granulomatous reactions developed around plain beads in immunized mice. In nonimmunized animals, both plain and antigen conjugated beads produced very small granulomas. Granuloma formation in sensitized animals was associated with suppressed delayed-type hypersensitivity reactions induced by the footpad injection of specific and nonspecific antigens. Lymph node cells from sensitized granuloma-bearing mice with cutaneous anergy showed suppressed specific and nonspecific antigen-induced proliferative responses in vitro. These cells also showed suppressed interleukin 2 production in response to specific antigen. Although no soluble suppressive factor was detected in granuloma extracts, suppressor cells were found in lymph nodes of granuloma-bearing mice, which could inhibit antigen-induced production of interleukin 2 by lymph node cells from immunized mice. Antigen-specific immunoglobulin G antibody production was not suppressed in immunized granuloma-bearing mice. Previous studies from our laboratory have demonstrated migration inhibition factor and interleukin 1 activities in aqueous extracts prepared from granuloma-bearing lungs of immunized mice. These results and the findings reported here indicate that granuloma formation and the associated anergy observed in this system are primarily expressions of cell-mediated immunity; selective suppression of in vivo and in vitro expressions of cell-mediated immunity in granuloma-bearing mice may be due to impaired antigen-induced interleukin 2 production; and such impairment is caused by suppressor cells.     

Metabolism of n-3 polyunsaturated fatty acids and modification of phospholipids in cultured rabbit aortic smooth muscle cells

The metabolism of the linolenic acid family (n-3) of fatty acids, e.g., linolenic, eicosapentaenoic, and docosahexaenoic acids, in cultured smooth muscle cells from rabbit aorta was compared to the metabolism of linoleic and arachidonic acids. There was a time-dependent uptake of these fatty acids into cells for 16 hr (arachidonic greater than docosahexaenoic, linoleic, eicosapentaenoic greater than linolenic), and the acids were incorporated mainly into phospholipids and triglycerides. Eicosapentaenoic and arachidonic acids were incorporated more into phosphatidylethanolamine and phosphatidylinositol plus phosphatidylserine and less into phosphatidylcholine than linolenic and linoleic acids. Docosahexaenoic acid was incorporated into phosphatidylethanolamine more than linolenic and linoleic acids and into phosphatidylinositol plus phosphatidylserine less than eicosapentaenoic and arachidonic acids. Added linolenic acid accumulated mainly in phosphatidylcholine and did not decrease the arachidonic acid content of any phospholipid subfraction. Elongation-desaturation metabolites of linoleic acid did not accumulate. Cells treated with eicosapentaenoic acid accumulated both eicosapentaenoic and docosapentaenoic acids mainly in phosphatidylethanolamine and the arachidonic acid content was decreased. Added docosahexaenoic acid accumulated mainly in phosphatidylethanolamine and decreased the content of both arachidonic and oleic acids. The following conclusions are drawn from these results. The three n-3 fatty acids are utilized differently in phospholipids. The arachidonic acid content of phospholipids is reduced by eicosapentaenoic and docosahexaenoic acids, but not by linolenic acid. Smooth muscle cells have little or no desaturase activity, but have significant elongation activity for polyunsaturated fatty acids.     

Estrogen-mediated induction of a vitellogenin-specific nonhistone chromatin protein in the male chicken liver

Summary Non-histone chromatin proteins prepared from the livers of estrogen-treated and nontreated male chickens were compared by reverse-phase high performance liquid chromatography (RP-HPLC), followed by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The results revealed that the hormone-treated male liver chromatin contained a specific protein corresponding to the vitellogenin-specific protein previously purified from the liver of egg-laying hens (Nakayama 1985). The chicken protein, purified further by gel-filtration high performance liquid chromatography (GF-HPLC), showed specific binding activity to DNA fragments carrying a part of the vitellogenin gene. On the basis of similarities in the elution patterns from GF-HPLC and RP-HPLC as well as in the mobility on SDS-PAGE, we concluded that this hormone-induced protein in the male chicken liver was identical to the vitellogenin-specific protein identified in the hen liver, and assumed it to be a specific regulatory protein for the vitellogenin gene expression. The amino acid composition of this chicken protein has been determined.     

The Effect of Ageing on Bud Differentiation in the Moss, Physcomitrium sphaericum

In the moss Physcomitrium sphaericum, we examined the numberof buds per filament, the position of buds, and the ratio ofbud-differentiated filaments when treated with cytokinin, inrelation to the increase in the number of cells per filament. When filaments of a young protonema were treated with cytokinin,many filaments did not differentiate buds. As the number ofcells in a filament increased, both the mean number of budsper filament and the ratio of bud-differentiated filaments increased.However, the position of bud differentiation was unaffectedby application of cytokinin. A higher concentration of cytokininincreased the mean number of buds per filament and the ratioof bud-differentiated filaments. The relationship between cytokinin, ageing of filaments andthe ability to differentiate buds is discussed. (Received June 17, 1985; Accepted September 9, 1985)     

Postischemic Cerebral Lipid Peroxidation In Vitro: Modification by Dietary Vitamin E

Using an in vitro system, we studied the effect of postischemic reoxygenation on cerebral lipid peroxidation in relation to the dietary intake of vitamin E (VE) in rats. Homogenates prepared from VE-deficient, -normal, and -supplemented brains, which were previously rendered ischemic for 30 min by decapitation, were incubated under air or nitrogen gas for 60 min. The extent of peroxidation in brain tissue was estimated by a thiobarbituric acid (TBA) test and by diene conjugation in total lipid extracts. The brain levels of alpha-tocopherol and of total and free fatty acids (FAs) were also determined. Aerobic incubation increased TBA reactants in all dietary groups; the effect was largest in the VE-deficient group, intermediate in the VE-normal group, and smallest in the VE-supplemented group. In contrast, nitrogen incubation did not alter the basal levels of TBA reactants except for a small rise associated with VE deficiency. Conjugated dienes changed in parallel with TBA reactants. alpha-Tocopherol decreased after aerobic incubation and also, to a lesser degree, after nitrogen incubation in each dietary group. Only in the reoxygenated samples of the VE-deficient group was there a significant fall in total polyunsaturated FAs. The levels of free FAs continuously increased throughout ischemia and subsequent incubation. However, the level of free polyunsaturated FAs was similar after aerobic and nitrogen incubation in each dietary group, and was not affected by VE. Thus, cerebral reoxygenation after ischemia propagates peroxidative reactions within esterified polyunsaturated FAs. The modification by VE of reoxygenation-induced lipid peroxidation suggests free radical mediation.