Hormonal regulation of the alpha-ketoglutarate dehydrogenase complex in the isolated perfused rat liver

The metabolic flux through the alpha-ketoglutarate dehydrogenase reaction in perfused livers was monitored by measuring the rate of 14CO2 production from [1-14C]alpha-ketoglutarate. The rates of 14CO2 production and glucose production from [1-14C]alpha-ketoglutarate were increased with increasing perfusate alpha-ketoglutarate concentrations. Vasopressin, angiotensin II, and the alpha 1-adrenergic agonist phenylephrine stimulated transiently by 2.5-fold the metabolic flux through the alpha-ketoglutarate dehydrogenase reaction in the presence and absence of Ca2+ in the perfusion medium. High concentrations of glucagon (1 x 10(-8) M) and 8-p-chlorophenylthio-cAMP (100 microM) (data not shown) also stimulated transiently the metabolic flux through the alpha-ketoglutarate dehydrogenase reaction. However, lower glucagon concentrations (1 x 10(-9) M) stimulated the rate of 14CO2 production from [1-14C]alpha-ketoglutarate only under conditions optimized to fix the cellular oxidation-reduction state at an intermediate level, when glucagon (1 x 10(-9) M)-mediated elevation of cAMP content was greater than that observed under highly oxidizing and reducing conditions. These data indicate that agonists which increase cytosolic free Ca2+ levels stimulate the metabolic flux through the alpha-ketoglutarate dehydrogenase complex. Furthermore, the data presented here demonstrate for the first time that physiological glucagon concentrations stimulate the metabolic flux through the alpha-ketoglutarate dehydrogenase reaction only under conditions known to be optimal for glucagon-mediated Ca2+ mobilization in the isolated perfused rat liver.     

Oxidative metabolism of spironolactone: evidence for the involvement of electrophilic thiosteroid species in drug-mediated destruction of rat hepatic cytochrome P450

In a preliminary paper [Decker et al. (1986) Biochem. Biophys. Res. Commun. 136, 1162] we have shown that the antimineralocorticoid spironolactone (SPL) preferentially inactivates dexamethasone (DEX) inducible rat hepatic cytochrome P450p isozymes in a suicidal manner. These findings are now confirmed, and the kinetic characteristics of such a process are detailed. In an effort to elucidate the mechanism of SPL-mediated inactivation of cytochrome P450, we have examined the metabolism of SPL in vitro. Incubation of [14C]SPL and NADPH with liver microsomes prepared from DEX-pretreated rats results in the formation of several polar metabolites separable by HPLC with UV detection. This process is found to be dependent on NADPH, O2, SPL, and enzyme concentration, as well as temperature. Furthermore, metabolite formation was significantly attenuated by P450 inhibitors CO and n-octylamine. Mass spectral analysis (thermospray LC/MS, FAB/MS, and FAB/MS/MS) of the two most prominent polar metabolites indicated that these compounds had molecular weights that corresponded to the sulfinic and sulfonic acid derivatives of deacetyl-SPL (SPL-SH). These findings document the formation of previously unreported polar metabolites of SPL by rat liver microsomes enriched in cytochrome P450p and implicate a role for this isozyme in the oxidation of the thiol moiety of deacetyl-SPL. The detection of such metabolites also implicates a catalytic trajectory that includes the thiyl radical and/or sulfenic acid species as a plausible protagonist in drug-mediated inactivation of cytochrome P450p.     

Contribution of the mesophilic fungi of different spices in Egypt

Thirty-eight genera and 81 species of fungi were isolated and identified from 120 samples of 24 kinds of spices collected from different places at Assiut Governorate, Egypt. Predominant genera wereAspergillus (25 species) andPenicillium (7 species) of whichA. flavus, A. niger, A. ochraceus, A. fumigatus, A. flavus var.columnaris, A. terreus, P. chrysogenum andP. corylophilum were the most commonly occurring.     

Glycerol production by two filamentous fungi grown at different ionic and nonionic osmotics and cheese whey

Glycerol production by a highly glycerol-producing local isolate (Eurotium amstelodami) and a standard reference isolate (Aspergillus wentii) was markedly enhanced by high saline media. Glycerol concentration depended on the external osmotic. Thus, the highest glycerol concentration was found in the presence of NaCl, followed by KCl, with considerably lower values for MgCl₂ and CaCl₂ saline media. With glucose (5–50%) used as a nonionic osmotic, low levels of glycerol were obtained and the main pool of polyols was mannitol. Glycerol production was gradually increased with the increase of NaCl concentration of cheese whey, reaching maxima by both organisms when whey was supplemented with 8% NaCl (total of 16% NaCl). The quantity of glycerol produced byA. wentii was twice higher than that obtained byE. amstelodami on whey treated with 8% NaCl.     

Accumulation of sugar alcohols by filamentous fungi

Five hundred isolates of different xerophilic and non-xerophilic fungi belonging to 10 genera and 74 species were screened for alditol (sugar alcohol) accumulation. Ninety-two of the isolates failed to grow on a salt medium, most of the isolates (408) produced alditols; 348,44 and 16 of them produced low, moderate and high levels of alditols, respectively. The high alditol producers belonged to five species ofAspergillus, six species ofEurotium andFennellia flavipes. Glycerol andd-mannitol were the main constituents of alditol pools of the 16 high alditol producers.d-Arabinitol andmeso-erythritol were also formed but at low concentrations by several of the tested isolates.     

Increase in the number of atrial natriuretic hormone receptors in regenerating rat liver.

Forty-eight hours after partial (approximately 67%) hepatectomy the activity of the particulate guanylate cyclase was increased by 2-fold in the regenerating rat liver. This increase was not an artifact of membrane isolation procedures, and as determined by 125I-labeled Tyr-28 atrial natriuretic hormone-(1-28) ANF binding, was accompanied by a 2-fold increase in the number of ANF receptors. The Kd of the receptors in membranes of regenerating livers was not significantly different from the Kd of the receptors in livers of sham-operated rats. The linear synthetic descysteine analog of ANF, analog I, which binds only to the 66-kDa receptors, displaced approximately 40% of the specifically bound 125I-ANF in liver membranes from both hepatectomized and sham-operated (control) animals. Affinity cross-linking studies with 125I-ANF confirmed the increase in the 116-kDa ANF receptor in membranes of regenerating livers. In perfused livers derived from control and hepatectomized animals, the basal rates of cGMP production were not significantly different. However, atriopeptin II-stimulated cGMP production was twice as great in regenerating livers as compared with controls. These data demonstrate that the increase in particulate guanylate cyclase activity observed during liver regeneration is due to an increase in the 116-kDa ANF receptor-associated activity. Additionally, our data demonstrate that the regenerating rat liver may be a valuable model with which to study the role of the hepatic ANF receptor/particulate guanylate cyclase.     

S-(N-methylcarbamoyl)glutathione: a reactive S-linked metabolite of methyl isocyanate

S-(N-methylcarbamoyl)glutathione, a chemically-reactive glutathione conjugate, has been isolated from the bile of rats administered methyl isocyanate and characterized, as its N-benzyloxycarbonyl dimethylester derivative, by tandem mass spectrometry. The ability of this glutathione adduct to donate an N-methylcarbamoyl moiety to the free -SH group of cysteine was evaluated in vitro with the aid of a highly specific thermospray LC/MS assay procedure. The glutathione adduct reacted readily with cysteine in buffered aqueous media (pH 7.4, 37 degrees C) and after 2 hr, 42.5% of the substrate existed in the form of S-(N-methylcarbamoyl)cysteine. The reverse reaction, i.e. between the cysteine adduct and free glutathione, also took place readily under these conditions. It is concluded that conjugation of methyl isocyanate with glutathione in vivo affords a reactive S-linked product which displays the potential to carbamoylate nucleophilic amino acids. The various systemic toxicities associated with exposure of animals or humans to methyl isocyanate could therefore be due to release of the isocyanate from its glutathione conjugate, which thus may serve as a vehicle for the transport of methyl isocyanate in vivo.     

A high-fat diet rich in corn oil exaggerates the infarct size and memory impairment in rats with cerebral ischemia and is associated with suppressing osteopontin and Akt,and activating GS3Kβ, iNOS,and NF-κB

Journal of Physiology and Biochemistry - The increase in osteopontin (OPN) levels after stroke induces neural protection by activating Akt signaling and inhibiting GS3Kβ, iNOS, and NF-κB....     

Synthesis of Some New Pyrazoline-Based Thiazole Derivatives and Evaluation of Their Antimicrobial,Antifungal, and Anticancer Activities

Russian Journal of Bioorganic Chemistry - 3-(2-Thienyl)-5-aryl-1-thiocarbamoyl-2-pyrazolines were reacted with chloroacetone derivatives and hydrazonyl chloride derivatives in ethanol to afford the...