Heme geometry in the 10 K photoproduct from sperm whale carbonmonoxymyoglobin

We have measured the Soret band of the photoproduct obtained by complete photolysis of sperm whale carbonmonoxymyoglobin at 10 K. The experimental spectrum has been modeled with an analytical expression that takes into account the homogeneous bandwidth, the coupling of the electronic transition with both high and low frequency vibrational modes, and the effects of static conformational heterogeneity. The comparison with deoxymyoglobin at low temperature reveals three main differences. In the photoproduct, the Soret band is shifted to red. The band is less asymmetric, and an enhanced coupling to the heme vibrational mode at 674 cm⁻¹ is observed. These differences reflect incomplete relaxation of the active site after ligand dissociation. The smaller band asymmetry of the photoproduct can be explained by a smaller displacement of the iron atom from the mean porphyrin plane, in quantitative agreement with the X-ray structure analysis. The enhanced vibrational coupling is attributed to a subtle heme distortion from the planar geometry that is barely detectable in the X-ray structure.     

A novel family of linear plasmids with homology to plasmid pAL2-1 of Podospora anserina

Three recently isolated wild-type strains of the ascomycete Podospora anserina were analyzed for the presence of linear mitochondrial plasmids. In one of these strains, designated Wa6, at least 12 distinct plasmid-like elements were identified. From molecular analyses a minimum number of 78 individual linear molecules with proteins bound to their 5′ ends was estimated. In addition, the different members of this family of typical linear plasmids were shown to possess a common central region and terminal sequences which differ from one plasmid to another due to the presence of different numbers of a 2.4 kb sequence module. Finally, the pWa6 plasmids share a high degree of sequence similarity with pAL2-1, a linear plasmid previously identified in mitochondria of a long-lived mutant of P.anserina. A mechanism is proposed which explains the generation of these distinct, closely related extrachromosomal genetic traits.     

Screening for a novel enzyme hydrolysing l-carnitine amide

In an extended screening using d,l-carnitine amide as carbon or nitrogen source about 1300 strains were obtained by enrichment culture. Of these, 65 strains possessed carnitine amidase activities. A single strain was identified as containing an enzyme able to hydrolyse only l-carnitine amide and yield carnitine of high enantiomeric purity (97) when incubated with the racemic substrate. During the initial optimisation of the culture conditions the volume activity could be improved 6.7-fold whereas the specific activity increased 3.6-fold. The enzyme is inducible by l-carnitine amide and carnitine and to a lesser degree also by -butyrobetaine and dehydrocarnitine. As judged by the fatty acids and quinone composition the strain belongs into the -subgroup of purple bacteria but has not yet been classified by the German Culture Collection into a known genus of bacteria. Correspondence to: M.-R. Kula     

Mechanisms of induction and repair of DNA double-strand breaks by ionizing radiation: Some contradictions

The various aspects of formation and repair of radiation-induced double-strand breaks (DSB) are summarized. Concerning the structure of DSB found in irradiated cells, enzymatic and microdosimetric analysis hints at complex damage of the DNA structure at the position of a DSB. With increasing LET, the DSB damage may be more complex than that induced by low-LET irradiation. Most of the DSB are repaired in the irradiated cell; apparently the kinetics of DSB repair and the fraction of unrejoined DSB determine cell survival or cell death. We do not know the details of the complex machinery of DSB repair; certaintly recombination processes are involved, but there are still contradictions between our current knowledge about the mechanisms of recombinational DSB repair and the observed kinetics.Dedicated to Prof. W. Jacobi on the occasion of his 65th birthday     

Chemical composition of lipopolysaccharides from Legionella bozemanii and Legionella longbeachae

Lipopolysaccharides (LPS) from Legionella bozemanii serogroup 1 and Legionella longbeachae serogroup 1 were subjected to chemical analyses. The lipid A part of both LPSs contained 2,3-dideoxy-2,3-diamino-d-glucose as major constituents and d-glucosamine and glycerol as minor constituents of the sugar backbone structure. Both LPSs exhibited a very complex fatty acid composition. Twenty amide-linked 3-hydroxy fatty acids were detected in LPS of L. longbeachae, whereas seventeen were encountered in LPS of L. bozemanii. Both LPSs contained nine ester-linked nonhydroxy fatty acids and the unique long-chain fatty acids 27-oxo-octacosanoic acid, 29-oxotriacontanoic acid, heptacosane-1,27-dioic acid and nonacosane-1,29-dioic acid. SDS-PAGE showed that L. bozemanii produced smooth-form LPS, whereas L. longbeachae LPS was mainly of the R-type. Composition analyses were in accordance with these electrophoretic patterns. d-Quinovosamine and l-fucosamine constituted 80 mol% of the polysaccharide part of L. bozemanii LPS. Other sugars identified were d-glucosamine, d-mannose, d-glucose, l-rhamnose, d-glycero-d-manno-heptose, l-glycero-d-mannoheptose, 2-keto-3-deoxy-octonic acid and glycerol. The polysaccharide chain from LPS of L. longbeachae appeared to be shorter, but composed of the same sugars except l-fucosamine. Both LPSs contained glycerol phosphate and glucosamine phosphate and L. longbeachae LPS contained in addition glucose phosphate.Abbreviations EI Electron impact - GlcN3N 2,3-Diamino-2,3-dideoxy-d-glucose - HPAEC High pH anion-exchange chromatography - Kdo 2-Keto-3-deoxy-octonic acid - LPS Lipopolysaccharide - PCP Phenol/chloroform/petroleum ether solvent - PED Pulsed electrochemical detection - PS Polysaccharide - TFA Trifluoroacetyl - TMS Trimethylsilyl     

Molecular response of the lipid headgroup to bilayer hydration monitored by 2H-NMR.

The effect of hydration on the conformation and dynamics of the phosphatidylcholine headgroup has been investigated by 2H-NMR measurements of liquid crystalline dioleoylphosphatidylcholine in multilamellar liposomes. Deuterium quadrupole splittings (delta nu Q) and spin-lattice relaxation rates (1/T1) were recorded for three selectively labeled headgroup segments (alpha, beta, and gamma) over the range of water/lipid mole ratios from 4 to 100. The smooth changes in delta nu Q and 1/T1 are found to essentially parallel each other and can be described by a single exponential decay function. Progressive hydration thus induces a concerted change in headgroup conformation together with an increase in its rate of motion (detected by delta nu Q and 1/T1, respectively). The enhanced mobility is partially due to a shift in the lipid phase transition temperature (as monitored by differential scanning calorimetry) and is furthermore attributed to an entropic contribution. It is concluded that the choline dipole becomes slightly raised in its average orientation into the aqueous layer and that the rate is increased at which the headgroup is fluctuating and protruding. The observed molecular changes can thus be accommodated within a model where the effective accessible headgroup volume expands with increasing hydration.