Alternative exon usage selectively determines both tissue distribution and subcellular localization of the acyl-CoA thioesterase 7 gene products

Acyl-CoA thioesterases (ACOTs) catalyze the hydrolysis of acyl-CoAs to free fatty acids and coenzyme A. Recent studies have demonstrated that one gene named Acot7, reported to be mainly expressed in brain and testis, is transcribed in several different isoforms by alternative usage of first exons. Strongly decreased levels of ACOT7 activity and protein in both mitochondria and cytosol was reported in patients diagnosed with fatty acid oxidation defects, linking ACOT7 function to regulation of fatty acid oxidation in other tissues. In this study, we have identified five possible first exons in mouse Acot7 (Acot7a–e) and show that all five first exons are transcribed in a tissue-specific manner. Taken together, these data show that the Acot7 gene is expressed as multiple isoforms in a tissue-specific manner, and that expression in tissues other than brain and testis is likely to play important roles in fatty acid metabolism. Received 5 February 2007: received after revision 3 April 2007; accepted 19 April 2007     

Identification and characterisation of two allelic forms of human alcohol dehydrogenase 2

The human alcohol dehydrogenase system is comprised of multiple forms that catalyse the oxidation/reduction of a large variety of alcohols and aldehydes. A transition that results in an Ile308Val substitution was identified in the human ADH2 gene by single-strand conformation polymorphism analysis. Screening a Swedish population revealed that Val308 was the most frequent allele (73%), and site-directed mutagenesis was used to obtain both allelozymes, which were expressed in Escherichia coli for characterisation. Thermostability was assayed by activity measurements and circular dichroism spectroscopy. The results showed that the 308Val substitution decreases protein stability, as compared to the Ile308 variant, an effect also demonstrated during prolonged storage. Ethanol, octanol, 12-hydroxydodecanoic acid and all-trans retinol were used as model substrates and, generally, slightly higher Km values were observed with Val at position 308. Finally, homology modelling, from mouse ADH2, further supported the decreased stability of the Val308 variant and located position 308 in the subunit interface of the molecule and in the vicinity of the active-site pocket entrance. In conclusion, the Ile308Val substitution represents a novel functional polymorphism within the human alcohol dehydrogenase gene cluster that may affect the metabolism of ethanol and other substrates.     

Effects of Carbon Content and Solidification Rate on the Thermal Conductivity of Grey Cast Iron

The thermal conductivity/diffusivity of pearlitic grey irons with various carbon contents was investigated by the laser flash method. The materials were cast in controlled thermal environments producing three dissimilar cooling rates. The cooling rates together with the carbon content largely influence the thermal conductivity of grey iron. Linear relationships exist between the thermal conductivity and the carbon content, the carbon equivalent, and the fraction of the former primary solidified austenite transformed into pearlite. The results show that the optimal thermal transport properties are obtained at medium cooling rates. Equations are given for the thermal conductivity of pearlite, solidified as pre-eutectic austenite, and the eutectic of grey iron. The thermal conductivity of pearlitic grey iron is modelled at both room temperature and elevated temperatures with good accuracy.     

L-arginine and pancreatic islet blood flow in anesthetized rats

The aim of the present study was to see if L-arginine, which induces insulin release and is a precursor of the endothelial-derived relaxing factor nitric oxide, affects whole pancreatic and/or islet blood flow. For this purpose, anesthetized male Sprague-Dawley rats were injected intravenously with either saline or L-arginine (25, 100 or 250 mg/kg body weight). All doses of arginine caused a slight increase in blood glucose concentration, while the highest dose (250 mg/kg body weight) also increased insulin concentration. However, no changes in either mean arterial blood pressure, whole pancreatic or islet blood flow could be discerned with any of the doses of arginine used. It is concluded that insulin release is not necessarily associated with an increased islet blood perfusion.     

The complete genome sequence of Francisella tularensis, the causative agent of tularemia

Francisella tularensis is one of the most infectious human pathogens known. In the past, both the former Soviet Union and the US had programs to develop weapons containing the bacterium. We report the complete genome sequence of a highly virulent isolate of F. tularensis (1,892,819 bp). The sequence uncovers previously uncharacterized genes encoding type IV pili, a surface polysaccharide and iron-acquisition systems. Several virulence-associated genes were located in a putative pathogenicity island, which was duplicated in the genome. More than 10% of the putative coding sequences contained insertion-deletion or substitution mutations and seemed to be deteriorating. The genome is rich in IS elements, including IS630 Tc-1 mariner family transposons, which are not expected in a prokaryote. We used a computational method for predicting metabolic pathways and found an unexpectedly high proportion of disrupted pathways, explaining the fastidious nutritional requirements of the bacterium. The loss of biosynthetic pathways indicates that F. tularensis is an obligate host-dependent bacterium in its natural life cycle. Our results have implications for our understanding of how highly virulent human pathogens evolve and will expedite strategies to combat them.