Homologues, Analysis

When yohimbine is heated with potash solution it is eonverted into potassium yohimbate, from which yohimbic acid (the forms yohimboie and yohimboaic are also used and noryohimbine), C20H24O3N2. H2O, is liberated by acetie acid it crystallises from water in lustrous prisms, m.p. 269° or 299° (dry, dec.), [ajo 138-8° (pyridine), and, on esterification with methyl alcohol and its homologues, reproduces yohimbine and its homologues, analysis of which by Field confirmed the view that yohimbine is methyl yohimbate, and has the formula assigned to it by Fourneau and Page. ... 

Moreover, some cDNA sequences were determined (see Genbank), such as Choi s in 1995 (U 25648 and U 25643), Sturzenbaum s in 1997 (AJ 223152). According the homologue analysis and sequence alignment, there could be some nonidentity homologs in sequences isolated from same earthworm species in different countries, this might be resulted from site-mutation occurred under dissimilar conditions. 

Ithough knowledge-based potentials are most popular, it is also possible to use other types potential function. Some of these are more firmly rooted in the fundamental physics of iteratomic interactions whereas others do not necessarily have any physical interpretation all but are able to discriminate the correct fold from decoy structures. These decoy ructures are generated so as to satisfy the basic principles of protein structure such as a ose-packed, hydrophobic core [Park and Levitt 1996]. The fold library is also clearly nportant in threading. For practical purposes the library should obviously not be too irge, but it should be as representative of the different protein folds as possible. To erive a fold database one would typically first use a relatively fast sequence comparison lethod in conjunction with cluster analysis to identify families of homologues, which are ssumed to have the same fold. A sequence identity threshold of about 30% is commonly... 

An application of an LC-SFC system has been demonstrated by the separation of non-ionic surfactants consisting of mono- and di-laurates of poly (ethyleneglycol) (23). Without fractionation in the precolumn by normal phase HPLC (Figure 12.18 (a)) and transfer of the whole sample into the SFC system, the different homologues coeluted with each other. (Figure 12.18(b)). In contrast with prior fractionation by HPLC into two fractions and consequent analysis by SFC, the homologues in the two fractions were well resolved (Figures 12.18(c) and 12.18(d)). 

Nirmalan, N., Cordeiro, N.J.V., Klager, S.L., Bradley, J.E. and Allen, J.E. (1999) Comparative analysis of glycosylated and non-glycosylated filarial homologues of the 20-kilodalton retinol binding protein from Onchocerca volvulus (Ov20). Infection and Immunity 67, 6239-6334. 

Commercial mixtures of surfactants comprise several tens to hundreds of homologues, oligomers and isomers of anionic, nonionic, cationic and amphoteric compounds. Therefore, their identification and quantification in the environment is complicated and cumbersome. The requirement of more specific analytical methods has prompted a replacement of many of the separate steps in traditional methods of analysis, usually non-chromatographic, by chromatographic tools. 

Since surfactants are commercially produced by means of large-scale chemical processes, complex mixtures of homologues and isomeric compounds, e.g. non-ionics of the alkylethoxylate type that may differ in length of alkyl as well as polyether chains, can result. The determination and differentiation of the products in quality control during production and trade is a somewhat easier task. However, more difficulties arise in the analysis of the compounds of these mixtures and formulations in environmental samples. 

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