Evolution im Reagensglas
: Mit der fehlerhaften Polymerasekettenreaktion als Methode der Zufallsmutagenese, einem effizienten Genexpressionssystem und einem Screening‐Test zur raschen Identifizierung ...enantioselektiver Katalysatoren läßt sich der
ee
‐Wert einer unselektiven Lipase‐katalysierten Esterhydrolyse schrittweise erhöhen (siehe Bild rechts).
magnified image
Evolution im Reagensglas: Mit der fehlerhaften Polymerasekettenreaktion als Methode der Zufallsmutagenese, einem effizienten Genexpressionssystem und einem Screening‐Test zur raschen Identifizierung ...enantioselektiver Katalysatoren läßt sich der ee‐Wert einer unselektiven Lipase‐katalysierten Esterhydrolyse schrittweise erhöhen (siehe Bild rechts).
The structure of the lipid A component of lipopolysaccharides isolated from two wild‐type strains (Fisher 2 and 7) and one rough mutant (PAC 605) of Pseudomonas aeruginosa was investigated using ...chemical analysis, methylation analysis, combined gas‐liquid chromatography/mass spectrometry, laser‐desorption mass spectrometry and NMR spectroscopy. The lipid A backbone was found to consist of a pyranosidic β1,6‐linked d‐glucosamine disaccharide β‐d‐GlcpN‐(1 → 6)‐d‐GlcpN, phosphorylated in positions 4′ and 1. Position 6′ of the β‐d‐GlcpN‐(1 → 6)‐d‐GlcpN disaccharide was identified as the attachment site of the core oligosaccharide and the hydroxyl group at C‐4 was not substituted. Lipid A of the three P. aeruginosa strains expressed heterogeneity with regard to the degree of acylation: a hexaacyl as well as a pentaacyl component were structurally characterized. The hexaacyl lipid A contains two amide‐bound 3‐O‐acylated (R)‐3‐hydroxydodecanoic acid groups 12:0(3‐OH) at positions 2 and 2′ of the GlcN dissacharide and two ester‐bound (R)‐3‐hydroxydecanoic acid groups 10:0(3‐OH) at positions 3 and 3′. The pentaacyl species, which represents the major lipid A component, lacks one 10:0(3‐OH) residue, the hydroxyl group in position 3 of the reducing GlcN residue being free. In both hexa‐ and pentaacyl lipid A the 3‐hydroxyl group of the two amide‐linked 12:0(3‐OH) residues are acylated by either dodecanoic (12:0) or (S)‐2‐hydroxydodecanoic acid 12:0(2‐OH), the lipid A species with two 12:0(2‐OH) residues, however, being absent. The presence of only five acyl residues in the major lipid A fraction may account for the low endotoxic activity observed with P. aeruginosa lipopolysaccharide.
