The expansion of the web and emergence of a large number of social networking sites (SNS) have empowered users to easily interconnect on a shared platform. A social network can be represented by a graph consisting of a set of nodes and edges connecting these nodes. The nodes represent the individuals/entities, and the edges correspond to the interactions among them. The tendency of people with similar tastes, choices, and preferences to get associated in a social network leads to the formation of virtual clusters or communities. Detection of these communities can be beneficial for numerous applications such as finding a common research area in collaboration networks, finding a set of likeminded users for marketing and recommendations, and finding protein interaction networks in biological networks. A large number of community-detection algorithms have been proposed and applied to several domains in the literature. This paper presents a survey of the existing algorithms and approaches for the detection of communities in social networks. We also discuss some of the applications of community detection.
The enzyme transferring the oligosaccharide from D~lPP-(GlcNAc)z(Man)~(Glc)~ to asparagine residues of glycoproteins has been solubilized from yeast membranes by extraction with detergents. Enzyme activity was tested by measuring transfer of the glycosyl moiety from D~IPP-['~C]saccharides to the hexapeptide Tyr-AsnLeu-Thr-Ser-Val. The rate of transfer was linear for 20 min, with about 40 of dolichyl-diphosphate-bound radioactivity transferred to the peptide.The solubilized enzyme has been characterized as follows :1. The enzyme is most efficiently solubilized (60 of the membrane-associated activity) by 0.5 (x Nonidet P40 at a protein/detergent ratio of 2. Octylglucoside solubilizes one third of the activity, but strongly inhibits the reaction if present in the test at a concentration of 1 %.2. Divalent cations are absolutely required. 1 mM Mn2+ is optimal; Mg2+ at a concentration of 10 mM yields only one third the activity observed with Mn2+.3. The enzyme transfers besides dolichyl-diphosphate-bound (GlcNAc)2(Man)9(Glc)3 also (GlcNAc)2(Man)l and ( G I~N A C )~ ; the rate decreases in this order. No transfer is observed from DolPP-(GlcNAc)z(Man)g and from DolPP-GlcNAc.4. The K , value for DolPP-(GlcNAc)2(Man)g(Glc)3 of 0.5 pM does not differ significantly l'rom that for DOIPP-(GICNAC)~ of 1.2 pM. A broad pH-optimum for the reaction with both substrates was found between 6.5 and 7.7. 5. However, a clear difference in K,,, values for the hexapeptide was observed with different dolichol-linked sugar derivatives. With DolPP-(GlcNAc)2 a peptide concentration of 0.6 mM resulted in half-maximal transfer rate, whereas 0.05 mM peptide were sufficient with DolPP-(GlcNAc)2(Man)~(Glc)3 as donor.
1. In a crude particulate fraction from yeast mannose is transferred from GDP-mannose to an endogenous "lipid" fraction, the monophosphates of dolichol-14 to dolichol-18. The same membrane fraction also catalyzes the mannosylation of glycoproteins. More than 80 of the total radioactivity in the glycoprotein fraction obtained from GDP-[14C]mannose is released by /?-elimination. The small-sized radioactive products of /?-elimination are mannose, mannobiose and mannotriose.2. Ageing of the particulate fraction leads to a drastic loss of mannosyl transfer activity from GDP-[14C]mannose to dolichol monophosphate. To the same extent the amount of [14C]mannose obtained after /?-elimination of the glycoproteins decreases. The amount of radioactive mannobiose and mannotriose is, however, much less affected.3. With decreasing GDP-mannose concentrations the amount of [14C]mannose obtained after /&elimination increases as compared to the amount of radioactive mannobiose and mannotriose. The Km-value for the incorporation of mannosyl groups directly linked to serine and/or threonine, therefore, is lower than the Km-value for the transfer of subsequent mannosyl residues.4. 6. The results are consistent with the assumption that dolichol monophosphate is involved in the mannosylation of a specific position in yeast glycoproteins, i.e. in the formation of mannosyl linkages to serine and/or threonine. The subsequent mannosylation proceeds directly from GDP-mannose in a reaction obligatorily requiring Mn2+.7. After /?-elimination of the methanol-insoluble material mannosylated in the presence of dolichol-monophosphate [14C]mannose the residual insoluble radioactivity is to a large extent transformed into dialyzable material by pronase. Mannose, therefore, is transferred from dolicholmonophosphate mannose also to glycoprotein positions not involving OH-groups of serine or threonine.Glycosylated lipids play a role in the biosynthesis of glycoproteins in animals [l -51, fungi [6,7] and plants [S]. The lipophilic component in all these cases is probably dolichol monophosphate [2,4,9,10].In Succhuvomyces cerevisiue the lipophilic mannosyl acceptor has been shown by mass spectroscopy to consist of the monophosphates of the whole family of dolichols with 14 to 18 isoprene units [lo]. From -~ his 60th birthday. mannosylated dolichol monophosphates the mannosyl group is transferred by yeast membranes to glycoproteins. Preliminary evidence has been presented [7] threonine, only the mannosyl residue directly linked to Dedicated to Professor Dr 0. Hoffmann-Ostenhof on Abbreviations. Dolichol-P, dolichol monophosphate; dolichol-P-Man, dolichol-monophosphate-mannose ; GDPthat within oligomannose chains linked to serine/ Man, guanosine-diphosphate-mannose.Eur. J. Biochem. 46 (1974)
STUDIES ON GLUCOSE PHOSPHORYLATION IN RAT LIVER 455 activities found earlier (Greenberg and Glick, 1960 a), after administration of ACTH, are consistent with the requirement of the hypothesis of Haynes and Berthet (1957) that TPNH generation be increased via the G-6-P dehydrogenase reaction, and that the source of G-6-P be G-l-P derived from glycogen. An increase in phosphorylase activity leading to production of G-l-P would also be expected, and this has been borne out by subsequent studies to be reported later.
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