A discrete time relativistic Toda lattice

Four integrable symplectic maps approximating two Hamiltonian flows from the relativistic Toda hierarchy are introduced. They are demostrated to belong to the same hierarchy and to examplify the general scheme for symplectic maps on groups equiped with quadratic Poisson brackets. The initial value problem for the difference equations is solved in terms of a factorization problem in a group. Interpolating Hamiltonian flows are found for all the maps.Comment: 32 pages, LaTe

Mutations in the 3 beta-hydroxysterol Delta(24)-reductase gene cause desmosterolosis, an autosomal recessive disorder of

Desmosterolosis is a rare autosomal recessive disorder characterized by multiple congenital anomalies. Patients with desmosterolosis have elevated levels of the cholesterol precursor desmosterol, in plasma, tissue, and cultured cells; this abnormality suggests a deficiency of the enzyme 3beta-hydroxysterol Delta24-reductase (DHCR24), which, in cholesterol biosynthesis, catalyzes the reduction of the Delta24 double bond of sterol intermediates. We identified the human DHCR24 cDNA, by the similarity between the encoded protein and a recently characterized plant enzyme--DWF1/DIM, from Arabidopsis thaliana--catalyzing a different but partially similar reaction in steroid/sterol biosynthesis in plants. Heterologous expression, in the yeast Saccharomyces cerevisiae, of the DHCR24 cDNA, followed by enzyme-activity measurements, confirmed that it encodes DHCR24. The encoded DHCR24 protein has a calculated molecular weight of 60.1 kD, contains a potential N-terminal secretory-signal sequence as well as at least one putative transmembrane helix, and is a member of a recently defined family of flavin adenine dinucleotide (FAD)-dependent oxidoreductases. Conversion of desmosterol to cholesterol by DHCR24 in vitro is strictly dependent on reduced nicotinamide adenine dinucleotide phosphate and is increased twofold by the addition of FAD to the assay. The corresponding gene, DHCR24, was identified by database searching, spans approximately 46.4 kb, is localized to chromosome 1p31.1-p33, and comprises nine exons and eight introns. Sequence analysis of DHCR24 in two patients with desmosterolosis revealed four different missense mutations, which were shown, by functional expression, in yeast, of the patient alleles, to be disease causing. Our data demonstrate that desmosterolosis is a cholesterol-biosynthesis disorder caused by mutations in DHCR2

Reinvestigation of peroxisomal 3-ketoacyl-CoA thiolase deficiency: identification of the true defect at the level of d-bifunctional protein

In this report, we reinvestigate the only patient ever reported with a deficiency of peroxisomal 3-ketoacyl-CoA thiolase (THIO). At the time when they were described, the abnormalities in this patient, which included accumulation of very-long-chain fatty acids and the bile-acid intermediate trihydroxycholestanoic acid, were believed to be the logical consequence of a deficiency of the peroxisomal β-oxidation enzyme THIO. In light of the current knowledge of the peroxisomal β-oxidation system, however, the reported biochemical aberrations can no longer be explained by a deficiency of this thiolase. In this study, we show that the true defect in this patient is at the level of d-bifunctional protein (DBP). Immunoblot analysis revealed the absence of DBP in postmortem brain of the patient, whereas THIO was normally present. In addition, we found that the patient had a homozygous deletion of part of exon 3 and intron 3 of the DBP gene, resulting in skipping of exon 3 at the cDNA level. Our findings imply that the group of single–peroxisomal β-oxidation–enzyme deficiencies is limited to straight-chain acyl-CoA oxidase, DBP, and α-methylacyl-CoA racemase deficiency and that there is no longer evidence for the existence of THIO deficiency as a distinct clinical entity

Phytanoyl-CoA hydroxylase from rat liver: protein purification and cDNA cloning with implications for the subcellular localization of phytanic acid alpha-oxidation

Phytanoyl-CoA hydroxylase (PhyH) catalyzes the conversion of phytanoyl-CoA to 2-hydroxyphytanoyl-CoA, which is the first step in the phytanic acid alpha-oxidation pathway. Recently, several studies have shown that in humans, phytanic acid alpha-oxidation is localized in peroxisomes. In rat, however, the alpha-oxidation pathway has been reported to be mitochondrial. In order to clarify this differential subcellular distribution, we have studied the rat PhyH protein. We have purified PhyH from rat liver to apparent homogeneity as judged by SDS-PAGE. Sequence analysis of two PhyH peptide fragments allowed cloning of the rat PHYH cDNA encoding a 38. 6 kDa protein. The deduced amino acid sequence revealed strong homology to human PhyH including the presence of a peroxisome targeting signal type 2 (PTS2). Heterologous expression of rat PHYH in Saccharomyces cerevisiae yielded a 38.6 kDa protein whereas the PhyH purified from rat liver had a molecular mass of 35 kDa. This indicates that PhyH is probably processed in rat by proteolytic removal of a leader sequence containing the PTS2. This type of processing has been reported in several other peroxisomal proteins that contain a PTS2. Subcellular localization studies using equilibrium density centrifugation showed that PhyH is indeed a peroxisomal protein in rat. The finding that PhyH is peroxisomal in both rat and humans provides strong evidence against the concept of a differential subcellular localization of phytanic acid alpha-oxidation in rat and huma