Evidence that biosynthesis of phosphatidylethanolamine, phosphatidylcholine, and triacylglycerol occurs on the cytoplasmic side of microsomal vesicles

Experiments were performed to localize the hepatic microsomal enzymes of phosphatidylcholine, phosphatidylethanolamine, and triacylglycerol biosynthesis to the cytoplasmic or lumenal surface of microsomal vesicles. Greater than 90 percent of the activities of fatty acid-CoA ligase (EC 6.2.1.3), sn-glycerol 3-phosphate acyltransferase (EC 2.3.1.15), lysophosphatidic acid acyltransferase, diacylglycerol acyltransferase (EC 2.3.1.20), diacylglycerol cholinephosphotransferase (EC 2.7.8.2), and diacylglycerol ethanolaminephosphotransferase (EC 2.7.8.1) was inactivated by proteolysis of intact microsomal vesicles. The phosphatidic acid phosphatase (EC 3.1.3.4) was not inactivated by any of the protease tested. Under conditions employed, <5 percent of the luminal mannose-6-phosphatase (EC 3.1.3.9) activity was lost. After microsomal integrity was disrupted with detergents, protease treatment resulted in a loss of >74 percent of the mannose-6-phosphatase activity. The latency of the mannose-6-phosphatase activity was not affected by protease treatment. Mannose-6-phosphatase latency was not decreased by the presence of the assay components of several of the lipid biosynthetic activities, indicating that those components did not disrupt the microsomal vesicles. None of the lipid biosynthetic activities appeared latent. The presence of a protease-sensitive component of these biosynthetic activities on the cytoplasmic surface of microsomal vesicles, and the absence of latency for any of these biosynthetic activities suggest that the biosynthesis of phosphatidylcholine, phosphatidylethanolamine, and triacylglycerol occurs asymmetrically on the cytoplasmic surface of the endoplasmic reticulum. The location of biosynthetic activities within the transverse plane of the endoplasmic reticulum is of particular interest for enzymes whose products may be either secreted or retained within the cell. Phosphatidylcholine, phosphatidylethanolamine, and triacylglycerol account for the vast majority of hepatic glycerolipid biosynthesis. The phospholipids are utilized for hepatic membrane biogenesis and for the formation of lipoproteins, and the triacylglycerols are incorporated into lipoproteins or accumulate within the hepatocyte in certain disease states (14). The enzymes responsible for the biosynthesis of these glycerolipids (Scheme I) from fatty acids and glycerol-3P have all been localized to the microsomal subcellular fraction (12, 16, 29, 30). Microsomes are derived from the endoplasmic reticulum and are sealed vesicles which maintain proper sidedness. (11, 22). The external surface of these vesicles corresponds to the cytoplasmic surface of the endoplasmic reticulum. Macromolecules destined for secretion must pass into the lumen of the endoplasmic reticulum (5, 23). Uncharged molecules of up to approximately 600 daltons are able to enter the lumen of rat liver microsomes, but macromolecules and charged molecules of low molecular weight do not cross the vesicle membrane (10, 11). Because proteases neither cross the microsomal membrane nor destroy the permeability barrier of the microsomal vesicles, only the enzymes and proteins located on the cytoplasmic surface of microsomal vesicles are susceptible to proteolysis unless membrane integrity is disrupted (10, 11). By use of this approach, several enzymes and proteins have been localized in the transverse plane of microsomal membranes (11). With the possible exception of cytochrome P 450, all of the enzymes and proteins investigated were localized asymmetrically by the proteolysis technique (11). By studies of this type, as well as by product localization, glucose-6-phosphate (EC 3.1.3.9) has been localized to the luminal surface of microsomal vesicles (11) and of the endoplasmic reticulum (18, 19). All microsomal vesicles contain glucose-6-phosphatase (18, 19) which can effectively utilize mannose-6-P as a substrate, provided the permeability barrier of the vesicles has been disrupted to allow the substrate access to the active site located on the lumenal surface (4). An exact correspondence between mannose- 6-phosphate activity and membrane permeability to EDTA has been established (4). The latency of mannose-6-phosphatase activity provides a quantitative index of microsomal integrity (4.) Few of the microsomal enzymes in the synthesis of phosphatidylcholine, phosphatidylethanolamine, and triacylglycerol have been solubilized and/or purified, and little is known about the topography of these enzymes in the transverse or lateral planes of the endoplasmic reticulum. An asymmetric location of these biosynthetic enzymes on the cytoplasmic or lumenal surface of microsomal vesicles may provide a mechanism for regulation of the glycerolipids to be retained or secreted by the cell, and for the biogenesis of asymmetric phospholipid bilayers. In this paper, we report investigations on the localization of all seven microsomal enzymes (Scheme I) in the biosynthesis of triacylglycerol, phosphatidylcholine, and phosphatidylethanolamine, using the protease technique with mannose-6-phosphatase serving as luminal control activity. The latency of these lipid biosynthetic enzymes was also investigated, using the latency of mannose-6-phosphatase as an index of microsomal integrity.     

Studies on 3-epimeric l-2-hexulose phenylosazones. Structure and anomeric configuration of the 3,6-anhydro-osazone derivatives obtained from l-xylo- and l-lyxo-2-hexulose phenylosazone

Dehydration of the 3-epimeric 2-hexulose phenylosazones l-xylo-hexulose phenylosazone and l-lyxo-hexulose phenylosazone afforded 3,6-anhydro-l-lyxo-2-hexulose phenylosazone (2) as the preponderant isomer from both. The identity of 2 was obtained by t.l.c., and by acetylation followed by comparison of the products. Acetylation of 2 with acetic anhydride-pyridine afforded the di-O-acetyl derivative 4, and further acetylation gave the N-acetyldi-O-acetyl derivative 5. Refluxing of 2 with copper sulfate afforded a C-nucleoside analog, namely, 2-phenyl-4-α-l-threofuranosyl-1,2,3-osotriazole (6). The anomeric configuration was determined by n.m.r. spectroscopy. The stereochemical course of the dehydration process and the mass spectra of compounds 2, 4, 5, and 6 are discussed.     

Adding Content to Contacts: Measurement of High Quality Contacts for Maternal and Newborn Health in Ethiopia,North East Nigeria,and Uttar Pradesh,India

BackgroundFamilies in high mortality settings need regular contact with high quality services, but existing population-based measurements of contacts do not reflect quality. To address this, in 2012, we designed linked household and frontline worker surveys for Gombe State, Nigeria, Ethiopia, and Uttar Pradesh, India. Using reported frequency and content of contacts, we present a method for estimating the population level coverage of high quality contacts.ConclusionsMeasuring content of care to reflect the quality of contacts can reveal missed opportunities to deliver best possible health care.     

Colon electrical stimulation: potential use for treatment of obesity

Obesity is one of the most prevalent health problems in the United States. Current therapeutic strategies for the treatment of obesity are unsatisfactory. We hypothesized the use of colon electrical stimulation (CES) to treat obesity by inhibiting upper gastrointestinal motility. In this preliminary study, we aimed at studying the effects of CES on gastric emptying of solid, intestinal motility, and food intake in dogs. Six dogs, equipped with serosal colon electrodes and a jejunal cannula, were randomly assigned to receive sham-CES or CES during the assessment of: (i) gastric emptying of solids, (ii) postprandial intestinal motility, (iii) autonomic functions, and (iv) food intake. We found that (i) CES delayed gastric emptying of solids by 77%. Guanethidine partially blocked the inhibitory effect of CES on solid gastric emptying; (ii) CES significantly reduced intestinal contractility and the effect lasted throughout the recovery period; (iii) CES decreased vagal activity in both fasting and fed states, increased the sympathovagal balance and marginally increased sympathetic activity in the fasting state; (iv) CES resulted in a reduction of 61% in food intake. CES reduces food intake in healthy dogs and the anorexigenic effect may be attributed to its inhibitory effects on gastric emptying and intestinal motility, mediated via the autonomic mechanisms. Further studies are warranted to investigate the therapeutic potential of CES for obesity.     

Craniodental morphology and systematics of a new family of hystricognathous rodents (Gaudeamuridae) from the late eocene and early oligocene of Egypt

Background

Gaudeamus is an enigmatic hystricognathous rodent that was, until recently, known solely from fragmentary material from early Oligocene sites in Egypt, Oman, and Libya. Gaudeamus'' molars are similar to those of the extant cane rat Thryonomys, and multiple authorities have aligned Gaudeamus with Thryonomys to the exclusion of other living and extinct African hystricognaths; recent phylogenetic analyses have, however, also suggested affinities with South American caviomorphs or Old World porcupines (Hystricidae).

Methodology/Principal Findings

Here we describe the oldest known remains of Gaudeamus, including largely complete but crushed crania and complete upper and lower dentitions. Unlike younger Gaudeamus species, the primitive species described here have relatively complex occlusal patterns, and retain a number of plesiomorphic features. Unconstrained parsimony analysis nests Gaudeamus and Hystrix within the South American caviomorph radiation, implying what we consider to be an implausible back-dispersal across the Atlantic Ocean to account for Gaudeamus'' presence in the late Eocene of Africa. An analysis that was constrained to recover the biogeographically more plausible hypothesis of caviomorph monophyly does not place Gaudeamus as a stem caviomorph, but rather as a sister taxon of hystricids.

Conclusions/Significance

We place Gaudeamus species in a new family, Gaudeamuridae, and consider it likely that the group originated, diversified, and then went extinct over a geologically brief period of time during the latest Eocene and early Oligocene in Afro-Arabia. Gaudeamurids are the only known crown hystricognaths from Afro-Arabia that are likely to be aligned with non-phiomorph members of that clade, and as such provide additional support for an Afro-Arabian origin of advanced stem and basal crown members of Hystricognathi.     

Synthesis of N-bridgehead heterocycles from saccharide benzimidazoles

Treatment of D-arabino-tetritol-1-yl-benzimidazole with P-toluenesulfonyl chloride (1molequiv) in pyridine, afforded the N-bridgehead heterocycles, 2R,3R,4S-trihydroxy-1:2:3:4-tetrahydropyridino[1,2-a]benzimidazole. The structure of the latter compound was determined by acylation, (1)H, and (13)C NMR spectroscopy and mass spectrometry.