Effects of various squalene epoxides on coenzyme Q and cholesterol synthesis

2,3-Oxidosqualene is an intermediate in cholesterol biosynthesis and 2,3:22,23-dioxidosqualene act as the substrate for an alternative pathway that produces 24(S),25-epoxycholesterol which effects cholesterol homeostasis. In light of our previous findings concerning the biological effects of certain epoxidated all-trans-polyisoprenes, the effects of squalene carrying epoxy moieties on the second and third isoprene residues were investigated here. In cultures of HepG2 cells both monoepoxides of squalene and one of their hydrolytic products inhibited cholesterol synthesis and stimulated the synthesis of coenzyme Q (CoQ). Upon prolonged treatment the cholesterol content of these cells and its labeling with [³H]mevalonate were reduced, while the amount and labeling of CoQ increased. Injection of the squalene monoepoxides into mice once daily for 6 days elevated the level of CoQ in their blood, but did not change the cholesterol level. The same effects were observed upon treatment of apoE-deficient mice and diabetic GK-rats. This treatment increased the hepatic level of CoQ10 in mice, but the amount of CoQ9, which is the major form, was unaffected. The presence of the active compounds in the blood was supported by the finding that cholesterol synthesis in the white blood cells was inhibited. Since the ratio of CoQ9/CoQ10 varies depending on the experimental conditions, the cells were titrated with substrate and inhibitors, leading to the conclusion that the intracellular isopentenyl-PP pool is a regulator of this ratio. Our present findings indicate that oxidosqualenes may be useful for stimulating both the synthesis and level of CoQ both in vitro and in vivo.     

Quirks of dye nomenclature. 2. Congo red

The history, origin, identity, chemistry and uses of Congo red are described. Originally patented in 1884, Congo red soon found applications in dyeing cotton, as a pH indicator for chemists and as a biological stain. Unlike the majority of the 19th century synthetic dyes, it still is available commercially.     

Transbilayer movement of Glc-P-dolichol and its function as a glucosyl donor: protein-mediated transport of a water-soluble analog into sealed ER vesicles from pig brain

The results described in the accompanying article support the model in which glucosylphosphoryldolichol (Glc-P-Dol) is synthesized on the cytoplasmic face of the ER, and functions as a glucosyl donor for three Glc-P-Dol:Glc0-2Man9-GlcNAc2-P-P-Dol glucosyltransferases (GlcTases) in the lumenal compartment. In this study, the enzymatic synthesis and structural characterization by NMR and electrospray-ionization tandem mass spectrometry of a series of water-soluble beta-Glc-P-Dol analogs containing 2-4 isoprene units with either the cis - or trans - stereoconfiguration in the beta-position are described. The water- soluble analogs were (1) used to examine the stereospecificity of the Glc-P-Dol:Glc0-2Man9GlcNAc2-P-P-Dol glucosyltransferases (GlcTases) and (2) tested as potential substrates for a membrane protein(s) mediating the transbilayer movement of Glc-P-Dol in sealed ER vesicles from rat liver and pig brain. The Glc-P-Dol-mediated GlcTases in pig brain microsomes utilized [3H]Glc-labeled Glc-P-Dol10, Glc-P-(omega, c )Dol15, Glc-P(omega, t,t )Dol20, and Glc-P-(omega, t,c )Dol20as glucosyl donors with [3H]Glc3Man9GlcNAc2-P-P-Dol the major product labeled in vitro. A preference was exhibited for C15-20 substrates containing an internal cis -isoprene unit in the beta-position. In addition, the water-soluble analog, Glc-P-Dol10, was shown to enter the lumenal compartment of sealed microsomal vesicles from rat liver and pig brain via a protein-mediated transport system enriched in the ER. The properties of the ER transport system have been characterized. Glc- P-Dol10was not transported into or adsorbed by synthetic PC-liposomes or bovine erythrocytes. The results of these studies indicate that (1) the internal cis -isoprene units are important for the utilization of Glc-P-Dol as a glucosyl donor and (2) the transport of the water- soluble analog may provide an experimental approach to assay the hypothetical "flippase" proposed to mediate the transbilayer movement of Glc-P-Dol from the cytoplasmic face of the ER to the lumenal monolayer.      

Quirks of dye nomenclature. 9. Fluorescein

Adolf Baeyer announced the discovery of fluorescein in 1871 and named it after its most striking property, i.e., fluorescence. I describe here the synthesis of fluorescein. There are seven molecular species in both the solid state or in solution. I also summarize some of the diverse applications of the dye, both medical and nonmedical, which depend mostly on the facile detection of fluorescein at low concentration. Both animal and human toxicity are examined.     

Quirks of dye nomenclature. 1. Evans blue

The history, origin, identity, chemistry and use of Evans blue dye are described along with the first application to staining by Herbert McLean Evans in 1914. In the 1930s, the dye was marketed under the name, Evans blue dye, which was profoundly more acceptable than the ponderous chemical name.     

Substrate specificity of cis-prenyltransferase in rat liver microsomes.

Long chain cis-prenyltransferase in rat liver microsomes was studied using various allylic isoprenoid substrates. Microsomes could utilize trans-geranyl pyrophosphate, but not cis-geranyl pyrophosphate for polyprenyl pyrophosphate synthesis. Both trans, trans-farnesyl pyrophosphate and trans,cis-farnesyl pyrophosphate were used as substrates with Km values of 24 and 5 microM, respectively. trans,trans,cis-Geranylgeranyl pyrophosphate could be used as substrate with an apparent Km of 36 microM. trans,trans,trans-Geranylgeranyl pyrophosphate was also utilized as substrate, but with a very low affinity. After pulse labeling for 4 min, using [3H]isopentenyl pyrophosphate and trans,trans-farnesyl pyrophosphate, the only product formed was trans,trans,cis-geranylgeranyl pyrophosphate, which, upon chasing, yielded polyprenyl pyrophosphate. Independent of the nature of the substrate used, even in the case of polyprenyl 12-pyrophosphate and all-trans-nonaprenyl pyrophosphate, the chain lengths of the products were identical, i.e. polyprenyl pyrophosphates with 15-18 isoprene residues. Microsomes were able to synthesize trans,trans-farnesyl pyrophosphate using trans-geranyl pyrophosphate as substrate. The results indicate that rat liver microsomes contain a farnesyl pyrophosphate synthase activity and that the reaction catalyzed by cis-prenyltransferase may consist of two individual steps, i.e. synthesis of trans,trans,cis-geranylgeranyl pyrophosphate and elongation of this product to long chain polyprenyl pyrophosphates.     

Phosphatidylethanolamine:dolichol acyltransferase. Characterization and partial purification of a novel rat liver enzyme.

Incubation of rat or human post-heparin plasma with [3H]dolichol incorporated in liposomes consisting of dioleoyl phosphatidylcholine:dioleoyl phosphatidylethanolamine (3:1) resulted in the formation of radioactive dolichyl oleate. Non-heparinized plasma did not esterify dolichol, and, hence, the enzyme involved is probably associated with the cell surface and released into the blood by heparin. The major location of this activity was the liver, and, therefore, a partial purification of the enzyme from heparinized rat liver perfusates was performed using DEAE-Sephacel and heparin-Sepharose chromatography. The dolichol acyltransferase activity copurified with hepatic lipase activity in a lipid-protein complex of 350 kDa. Optimal acylation is achieved at pH 7.5 in the presence of 5% plasma and 20 mM Ca2+. Esterification can only be obtained when dolichol is present in a phospholipid bilayer, and the reaction is strongly stimulated by unsaturated phosphatidylethanolamine or phosphatidylserine. Radiolabeling experiments demonstrated that the primary acyl donor is phosphatidylethanolamine from which the fatty acid is transferred exclusively from position 1. Neither cholesterol nor retinol are esterified by the enzyme, and the reaction is not stimulated by acyl-CoA. Both the extracellular localization and the mechanism of transacylation clearly distinguish this new enzyme from the acyl-CoA:dolichol acyltransferase described earlier in microsomes.     

Differences among avian frugivores in seed dispersal to degraded habitats

Vertebrate frugivores enhance tropical forest regeneration by dispersing seeds into degraded areas. However, the importance of individual species as dispersers may vary within a community. Management and restoration would benefit from understanding which species are critical in moving native seeds into degraded habitats. We compared habitat composition of bird start and end locations for movement intervals based on mean gut passage times for the avian frugivore community on the island of Saipan. The proportion of movement intervals that began in intact, native forest varied among species, with Golden White‐eyes having the highest proportion. However, this species tended to remain in intact forest and only rarely crossed into degraded habitats. Bridled White‐eyes and Mariana Fruit Doves exhibited slightly higher rates of crossing from intact forest to degraded habitats, suggesting an ability to disperse native seeds to degraded areas. White‐throated Ground Doves were never recorded crossing from intact forest to degraded habitats. Despite having a low proportion of movement intervals beginning in intact forest, Micronesian Starlings showed a higher proportion and absolute number of movements from intact forest to degraded habitats, due to their propensity to move frequently, across long distances, and across habitat types. In this species‐poor frugivore network, seed dispersal into degraded habitats appears highly dependent on one species within the community. Regeneration of degraded lands may be severely hindered if this key disperser is lost.