Activation of rat liver cytosolic 3-hydroxy-3-methylglutaryl coenzyme A reductase kinase by adenosine 5'-monophosphate

Inactivation of 3-hydroxy-3-methylglutaryl Coenzyme A reductase by reductase kinase and ATP-Mg needs either ADP or 5'-AMP as cofactors. 5'-AMP is a more potent activator of cytosolic reductase kinase than ADP. This capacity is expressed by increasing not only the rate of reductase inactivation, but also the rate of reductase phosphorylation from [gamma-32P]ATP. Activation constants, Ka, for 5'-AMP and ADP are 20 microM and 420 microM respectively. Neither 3'-AMP nor 2'-AMP activate reductase kinase. Other nucleoside monophosphates like UMP, CMP and GMP cannot replace 5'-AMP as activators of reductase kinase.     

Non-local thermodynamic effects and efficiency of oxidative phosphorylation

A non-equilibrium thermodynamic model of oxidative phosphorylation is formulated, which allows us to take into account some non-local effects. In this way, we compute the influence of the tangential resistivity of the inner mitochondrial membrane to proton current, as well as that of the distance between active sites, on the stoichiometry and efficiency of energy conversion.     

Molecular cloning of covalently closed circular DNA of bovine leukemia virus

The two species of covalently closed circular DNA molecules of bovine leukemia virus were cloned in the lambda phage vector lambda gtWES X lambda B. Of the nine independent recombinant lambda-bovine leukemia virus clones that were analyzed, three were derived from the small and six were derived from the large circular molecules carrying, respectively, one and two copies of the long terminal repeat sequences. Comprehensive restriction endonuclease mapping of the unintegrated bovine leukemia virus and the cloned DNA molecules showed that eight of the nine clones carried viral information without any detectable deletions or insertions of more than ca. 50 base pairs. One of the nine clones, which carries a retroviral insert with one copy of the long terminal repeat, had a deletion of ca. 150 base pairs.     

Ultrastructure of the renal corpuscle of Testudo graeca (Chelonia). A comparison between hibernating and non-hibernating animals

The renal corpuscle of hibernating and non-hibernating Testudo graeca was studied by means of light and electron microscopy. Renal corpuscles are small and have a glomerular architecture similar to that found in other vertebrates with a limited glomerular filtration rate. In hibernating animals, unlike non-hibernating, some morphological changes took place. The cells of the renal corpuscle were densely packed, podocytes and parietal cells showed a marked cytoplasmic vacuolization, there was a highly developed capillary basement membrane and the endothelial and mesangial cells showed abundant dense granules. These morphological features apparently correspond to a vacuolar degeneration. They may also be the morphological basis of the decrease in the glomerular filtration rate observed during this period.     

Maternal 3:1 disjunction in a tranlocation 9/17

Summary An isochromosome of 15(q12) was found in a mentally retarded patient with behaviour disorders which included hyperactivity, short attention span, aggression, and autistic behaviour. There were only minor physical anomalies; he did not have the Prader-Willi syndrome.     

Liquid Nitrogen Freezing in Microbiological Assay Systems: I. Preservation of Lactobacillus leichmannii for Direct Use in the Vitamin B12 Assay

Suspensions of Lactobacillus leichmannii were stored in liquid nitrogen and were used as direct inocula in vitamin B₁₂ assays. Complete recovery of viable cells was obtained when the suspensions in basal B₁₂ medium were rapidly frozen by direct immersion into liquid nitrogen and rapidly thawed by agitating the suspensions in a water bath at 40 C. Greater than 90% destruction occurred when the suspensions were in saline. However, both suspensions were usable in the B₁₂ assay system. Assay results on a number of test materials indicated good correlation between freshly prepared suspensions and frozen suspensions in basal medium stored 3 months. Suspensions in saline stored for 1 year in liquid nitrogen showed no detectable difference from the first day after freezing. Suspensions frozen slowly at the rate of 1 degree per min from 4 to -40 C and subsequently immersed in liquid nitrogen had a longer lag period of growth and were not usable in the 18-hr assay incubation system. A major advantage of a stored inoculum for direct use in a microbiological assay is the reduced day-to-day variation in the inoculum.     

Successional dynamics of the phytoplankton in the lower part of the river Ebro

The temporal and spatial dynamics of phytoplankton have beenstudied in four sites located along the last 60 km of the riverEbro, over a period of 1 year. Diatoms and green algae werethe most abundant groups; blue-green algae were frequent onlyin autumn. Asterionella formosa dominated the winter phytoplanktonassemblages. In autumn, spring and early summer centric diatomswere dominant: Aulacoseira granulata (Ehr.) Simonsen in autunm;Cyclotella sp. p1., Skeletonema potamos (Weber) Hasle and StephanodisciLssp. p1. in spring. A great abundance of green algae was observedduring the summer, mainly in the lower sites. In the sites closerto the mouth, the spring maximum of centric diatoms extendedto the summer. Mainly in the downstream sites, a remarkablegrowth of Acrinocyclus normanii f. subsalsa (Juhl.-Daunf.) Hustedtand Stephanodiscus hantzschii f tenuis (Hust.) Hak. & Stoerm.was added to green algae in the late summer. As has been investigatedthrough a principal component analysis, the phytoplankton temporalsuccession and longitudinal differences between the sites maybe affected by the variations in flow and the increase of waterconductivity downstream; both factors seem to act together.The river is rather homogeneous with respect to the phytoplanktonassemblages during the winter and spring months, and from latespring to the following autumn, differences greatly increaseboth in time and downstream.     

L-lysine Transport in Chicken Jejunal Brush Border Membrane Vesicles

The properties of l-lysine transport in chicken jejunum have been studied in brush border membrane vesicles isolated from 6-wk-old birds. l-lysine uptake was found to occur within an osmotically active space with significant binding to the membrane. The vesicles can accumulate l-lysine against a concentration gradient, by a membrane potential-sensitive mechanism. The kinetics of l-lysine transport were described by two saturable processes: first, a high affinity-transport system (K _mA= 2.4 ± 0.7 μmol/L) which recognizes cationic and also neutral amino acids with similar affinity in the presence or absence of Na⁺ (l-methionine inhibition constant K_iA, NaSCN = 21.0 ± 8.7 μmol/L and KSCN = 55.0 ± 8.4 μmol/L); second, a low-affinity transport mechanism (K_mB= 164.0 ± 13.0 μmol/L) which also recognizes neutral amino acids. This latter system shows a higher affinity in the presence of Na⁺ (K_iB for l-methionine, NaSCN = 1.7 ± 0.3 and KSCN = 3.4 ± 0.9 mmol/L). l-lysine influx was significantly reduced with N-ethylmaleimide (0.5 mmol/L) treatment. Accelerative exchange of extravesicular labeled l-lysine was demonstrated in vesicles preloaded with 1 mmol/L l-lysine, l-arginine or l-methionine. Results support the view that l-lysine is transported in the chicken jejunum by two transport systems, A and B, with properties similar to those described for systems b ^0,+ and y⁺, respectively. Received: 14 August 1995/Revised: 2 April 1996     

The use of double fluorescence in situ hybridization to physically map the positions of 5S rDNA genes in relation to the chromosomal location of 18S-5.8S-26S rDNA and a C genome specific DNA sequence in the genus Avena.

A physical map of the locations of the 5S rDNA genes and their relative positions with respect to 18S-5.8S-26S rDNA genes and a C genome specific repetitive DNA sequence was produced for the chromosomes of diploid, tetraploid, and hexaploid oat species using in situ hybridization. The A genome diploid species showed two pairs of rDNA loci and two pairs of 5S loci located on both arms of one pair of satellited chromosomes. The C genome diploid species showed two major pairs and one minor pair of rDNA loci. One pair of subtelocentric chromosomes carried rDNA and 5S loci physically separated on the long arm. The tetraploid species (AACC genomes) arising from these diploid ancestors showed two pairs of rDNA loci and three pairs of 5S loci. Two pairs of rDNA loci and 2 pairs of 5S loci were arranged as in the A genome diploid species. The third pair of 5S loci was located on one pair of A-C translocated chromosomes using simultaneous in situ hybridization with 5S rDNA genes and a C genome specific repetitive DNA sequence. The hexaploid species (AACCDD genomes) showed three pairs of rDNA loci and six pairs of 5S loci. One pair of 5S loci was located on each of two pairs of C-A/D translocated chromosomes. Comparative studies of the physical arrangement of rDNA and 5S loci in polyploid oats and the putative A and C genome progenitor species suggests that A genome diploid species could be the donor of both A and D genomes of polyploid oats. Key words : oats, 5S rDNA genes, 18S-5.8S-26S rDNA genes, C genome specific repetitive DNA sequence, in situ hybridization, genome evolution.     

Molecular characterization of a fourth isoform of the catalytic subunit of protein phosphatase 2A from Arabidopsis thaliana

We have recently reported the existence of multiple isoforms of the catalytic subunit of protein phosphatase 2A (PP2A) in Arabidopsis thaliana and the molecular cloning of cDNAs encoding three of these proteins (PP2A-1, PP2A-2, PP2A-3). The reported cDNA encoding PP2A-3 was truncated at the 5 terminus, lacking a short fragment of the N-terminal coding sequence. We have now isolated a near full-length cDNA encoding the entire PP2A-3 protein (313 residues). The clone includes 188 nucleotides of 5-untranslated region, where a 44 bp long poly(GA) track is found. We also describe the cloning of a cDNA encoding a fourth isoform of PP2A (PP2A-4). The polypeptide contains 313 residues being 98% identical to PP2A-3 and only 80% identical to both PP2A-1 and PP2A-2. The mRNA for PP2A-4 is 1.4 kb in length and, although predominantly expressed in roots, it is also found in other organs. It is concluded that in A. thaliana the isoforms of PP2A can be grouped in two extremely conserved subfamilies.