Escherichia coli grew in a minimal medium on propionate as the sole carbon and energy source. Initially a lag phase of 4-7 days was observed. Cells adapted to propionate still required 1-2 days before growth commenced. Incorporation of (2-13C), (3-13C) or (2H3)propionate into alanine revealed by NMR that propionate was oxidized to pyruvate without randomisation of the carbon skeleton and excluded pathways in which the methyl group was transiently converted to a methylene group. Extracts of propionate-grown cells contained a specific enzyme that catalyses the condensation of propionyl-CoA with oxaloacetate, most probably to methylcitrate. The enzyme was purified and identified as the already-known citrate synthase II. By 2-D gel electrophoresis, the formation of a second propionate-specific enzyme with sequence similarities to isocitrate lyases was detected. The genes of both enzymes were located in a putative operon with high identities (at least 76% on the protein level) with the very recently discovered prp operon from Salmonella typhimurium. The results indicate that E. coli oxidises propionate to pyruvate via the methylcitrate cycle known from yeast. The 13C patterns of aspartate and glutamate are consistent with the further oxidation of pyruvate to acetyl-CoA. Oxaloacetate is predominantly generated via the glyoxylate cycle rather than by carboxylation of phosphoenolpyruvate.

Sequence variations of the KCNQ2 and KCNQ3 genes may contribute to the etiology of common idiopathic epilepsy syndromes.

Component D (HgdAB) of 2-hydroxyglutaryl-CoA dehydratase from Clostridium symbiosum was purified to homogeneity. It is able to use component A from Acidaminococcus fermentans (HgdC) to initiate catalysis together with ATP, Mg 2+ and a strong reducing agent such as Ti(III)citrate. Component D from C. symbiosum has a 6Â higher specific activity compared with that from A. fermentans and contains a second [4Fe±4S] cluster but the same amount of riboflavin 5 H -phosphate (1.0 per heterodimeric enzyme, m = 100 kDa). Mo Èssbauer spectroscopy revealed symmetric cube-type structures of the two [4Fe±4S] 2+ clusters. EPR spectroscopy showed the resistance of the clusters to reducing agents, but detected a sharp signal at g = 2.004 probably due to a stabilized flavin semiquinone. Three genes from C. symbiosum coding for components D (hgdA and hgdB) and A (hgdC) were cloned and sequenced. Primer extension experiments indicated that the genes are transcribed in the order hgdCAB from an operon only half the size of that from A. fermentans. Sequence comparisons detected a close relationship to the dehydratase system from A. fermentans and HgdA from Fusobacterium nucleatum, as well as to putative proteins of unknown function from Archaeoglobus fulgidus. Lower, but significant, identities were found with putative enzymes from several methanogenic Archaea and Escherichia coli, as well as with the mechanistically related benzoyl-CoA reductases from the Proteobacteria Rhodopseudomonas palustris and Thauera aromatica.

(R)-2-Hydroxyglutaryl-CoA dehydratase (HgdAB) from Acidaminococcus fermentans catalyses the reversible dehydration of its substrate to glutaconyl-CoA. The enzyme has to be activated by ATP, MgCl2, and Ti(III)citrate by an activator protein (HgdC) that is present in the organism at very low concentrations. Cell-free extracts of a recombinant Escherichia coli strain, in which hgdC was expressed, contained the activator with a specific activity of up to 45 U'/mg protein (1 U' is the amount of activator required to generate 1 U dehydratase activity under standard assay conditions). The recombinant protein was purified 44-fold to a specific activity of 2000 U'/mg. It is a homodimer (gamma 2, 54 kDa) and contains 4 mol non-heme iron and 3 mol inorganic sulfur. Under air, the activator has a half-life of seconds and even under strict anaerobic conditions it is very unstable. The amino acid sequence of the activator shows similarities to the ATP-binding motifs of several kinases. The dehydratase component was purified from its natural source revealing a heterodimer (alpha beta, 100 kDa) that contains 4 mol non-heme iron, 4 mol inorganic sulfur, 0.3 mol riboflavin, and 1 mol FMN. A mechanism is proposed in which an iron-sulfur cluster or a flavin donates one electron to the thiolester of the substrate (R)-2-hydroxyglutaryl-CoA. The resulting ketyl may eliminate the adjacent hydroxyl group yielding an enoxy radical from which the beta-hydrogen is abstracted as a proton leading to the ketyl of glutaconyl-CoA. In the final step, the latter is oxidized to the product, whereby the reduced enzyme is regenerated. It is suggested that during the activation step, the electron of this cycle is fed into the enzyme by Ti(III)citrate and energized by hydrolysis of ATP; both functions are apparently catalysed by the activator. The enzyme remains in this activated state for several turnovers, which may explain the requirement of only catalytic amounts of ATP and substoichiometric amounts of activator (dehydratase/activator ratio approximately 200:1). The oxidants 4-nitrobenzoate, 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone or chloramphenicol (all at concentrations greater than or equal to 1 microM) may trap this electron resulting in a reversible, transient inactivation of the dehydratase.

This study describes the technical handling and the diagnostic evaluation of skin biopsies in order to standardize the assessment of the delicate morphologic abnormalities that are found in patients with spontaneous cervical artery dissections (sCAD). Skin biopsies from 126 patients with sCAD and from 29 healthy relatives were analyzed. The morphology of the connective tissue was normal in 54 patients with sCAD (43%) and aberrant in 72 patients with sCAD (57%). These latter patients were classified into three groups: in 43 patients, we repeatedly observed composite collagen fibrils and elastic fibers with fragmentation and minicalcifications. In 13 further patients, the dermis was significantly thinner than in healthy subjects. The collagen fibers contained fibrils with highly variable diameters. In a third group of 16 sCAD patients, the abnormalities were restricted to the elastic fibers (with fragmentation and minicalcifications) without significant alterations in the morphology of the collagen fibrils. The finding of different morphologic classes of aberrations among patients suggests that the connective tissue defects are genetically heterogeneous. The segregation of the connective tissue phenotype in three families suggested an autosomal dominant pattern of inheritance.