Involvement of melanocortin receptor accessory proteins (MRAPs) in the function of melanocortin receptors.

The melanocortin system integrates different agonists, competitive or inverse agonists, and receptors. Recent investigations have also discovered a specific system of melanocortin receptor accessory proteins (MRAPs) that are involved in the regulation of the functional expression of these receptors. MRAP1 mutations are responsible for type 2 familial glucocorticoid deficiency (FGD2), a rare autosomal disorder characterized by high plasma adrenocorticotropin hormone (ACTH) levels but severe cortisol deficiency. ACTH binds melanocortin 2 receptor (MC2R), a G protein-coupled receptor, in the adrenal gland to promote corticosteroid synthesis. In the absence of MRAP1, MC2R cannot translocate from the endoplasmic reticulum to the plasma membrane and ACTH-induced signaling is extinguished. A second MRAP protein, called MRAP2, also modulates MC2R activity. MRAPs also interact with the other melanocortin receptors, adjusting their pharmacological properties. In this paper, we briefly review the MRAP system and its interaction with melanocortin receptors.

Preliminary study of the pyrolysis of steam classified municipal solid waste.

Steam classified municipal solid waste (MSW) has been studied for use as a combustion fuel, feedstock for composting, and cellulytic enzyme hydrolysis. A preliminary study has been conducted using a prototype plasma arc pyrolysis system (in cooperation with Plasma Energy Applied Technology Inc., Huntsville, AL) to convert the steam classified MSW into a pyrolysis gas and vitrified material. Using a feed rate of 50 lbs/h, 300 lbs of the material was pyrolysized. The major components of this pyrolysis gas were H(2), CO, and CO(2). A detailed presentation of the emission data along with details on the system used will be presented.

Chemistry and adsorption-desorption properties of manganese oxides deposited in Forehill Water Treatment Plant, Grampian, Scotland.

Manganese oxide coatings on sand particles within filtration beds from a water treatment plant in Grampian, Scotland were examined to determine their control on metal mobility. This study first sought to characterise the oxides, notably their mineralogy and metal content, to provide a foundation for studies on the adsorption of dissolved metals from the treated water by the oxides. The oxides were examined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and analysed by flame atomic absorption spectrophotometry (AAS). These techniques showed the oxide coatings were amorphous but uniformly distributed over each sand grain. The oxides were selectively removed from the sand grains prior to analysis by AAS using a hydroxylamine hydrochloride selective leaching method. The compositional range of the extracts was 100-150 mg L(-1) Mn; 30-55 mg L(-1) Fe; 17-56 mg L(-1) Ca; 4.6-7.0 mg L(-1) Ni; 4.6-6.8 mg L(-1) Zn and 1.3-5.7 mg L(-1) Mg. When these results are expressed as mg of metal per mg of Mn, the metal content of the oxides is remarkably uniform: 0.25-0.37 mg Fe; 0.14-0.35 mg Ca; 0.035-0.042 mg Ni; 0.035-0.040 mg Zn; 0.01-0.04 mg Mg. The greatest metal concentrations were consistently found in the upper 3 cm of the filtration bed, and these decrease with increasing depth. After the beds are cleaned a more uniform distribution of metals occurs throughout the bed. The metals taken up by the manganese coating are retained over a wide pH range with the exception of Ca and Mg which desorb to a significant extent. The percentage of calcium and magnesium lost from the coating ranges from 30-94%, the amount being dependent on the final pH of the solution. The presence of manganese oxide in the filtration beds appears to be advantageous in terms of removal of transition metals from the treated water.

Investigation of the lignin-degrading activity of Serratia marcescens: biochemical screening and ultrastructural evidence.

Forty-one morphologically distinct bacterial isolates were developed from six lignin-containing environments. Each isolate was initially screened for potential lignin-degrading activity using relative growth on a lignocellulosic substrate and relative decolorization of a polymeric dye. Screened isolates were then tested for the ability to oxidize various lignin-related monomers, and the dimers anisoin and veratrylglycerol-beta-guaiacyl ether. Although most of the isolates oxidized the monomers, only two successfully oxidized the dimers. The dimer-degrading isolates were tested for extracellular activity against the beta-O-4 dimer veratryl-glycerol-beta-guaiacyl ether. No activity was detected for the isolates. Phanerochaete chrysosporium Burds used as a positive control demonstrated a high degree of activity in each assay. Extensive ultrastructural studies of lignocellulose alteration by the dimer-degrading isolates were conducted via light and transmission electron microscopy. These studies indicate that one of the isolates, identified as Serratia marcescens, is capable of degrading highly lignified secondary cell wall components. This activity is localized, apparently requiring direct contact between cells and substrate, which could be facilitated by an associated glycocalix. The results of the dimer degradation assays concur with the characterization of the responsible enzyme system as being membrane associated.

Reconstitution of the Escherichia coli pyruvate dehydrogenase complex.

The binding of pyruvate dehydrogenase and dihydrolipoyl dehydrogenase (flavoprotein) to dihydrolipoyl transacetylase, the core enzyme of the E. coli pyruvate dehydrogenase complex [EC 1.2.4.1:pyruvate:lipoate oxidoreductase (decaryboxylating and acceptor-acetylating)], has been studied using sedimentation equilibrium analysis and radioactive enzymes in conjunction with gel filtration chromatography. The results show that the transacetylase, which consists of 24 apparently identical polypeptide chains organized into a cube-like structure, has the potential to bind 24 pyruvate dehydrogenase dimers in the absence of flavoprotein and 24 flavoprotein dimers in the absence of pyruvate dehydrogenase. The results of reconstitution experiments, utilizing binding and activity measurements, indicate that the transacetylase can accommodate a total of only about 12 pyruvate dehydrogenase dimers and six flavoprotein dimers and that this stoichiometry, which is the same as that of the native pyruvate dehydrogenase complex, produces maximum activity. It appears that steric hindrance between the relatively bulky pyruvate dehydrogenase and flavoprotein molecules prevents the transacetylase from binding 24 molecules of each ligand. A structural model for the native and reconstituted pyruvate dehydrogenase complexes is proposed in which the 12 pyruvate dehydrogenase dimers are distributed symmetrically on the 12 edges of the transacetylase cube and the six flavoprotein dimers are distributed in the six faces of the cube.

A kinetic study of dihydrolipoyl transacetylase from bovine kidney.

The mammalian pyruvate dehydrogenase complex contains a core, consisting of dihydrolipoyl transacetylase, to which pyruvate dehydrogenase and dihydrolipoyl dehydrogenase are joined. This report describes studies on the kinetic mechanism of the transacetylase-catalyzed reaction between [1-14C]acetyl-CoA and dihydrolipoamide. This reaction appears to be a model of the physiological reaction, in which the acetyl group is transferred from the S-acetyldihydrolipoyl moiety, bound covalently to the transacetylase, to CoA. The model reaction is not affected by pyruvate dehydrogenase or dihydrolipoyl dehydrogenase, their substrates and products, or by removal of the covalently bound lipoyl moiety. These findings, together with the results of initial velocity, product inhibition, and dead-end inhibition studies, indicate that the model reaction and, apparently, the physiological reaction as well, proceeds via the Random Bi Bi (rapid equilibrium) mechanism. It appears that at the catalytic center of the transacetylase there are two adjacent sites, one that binds CoA and acetyl-CoA and another that binds dihydrolipoamide and S-acetyldihydrolipoamide (or the corresponding forms of the covalently bound lipoyl moiety.