Possible sites of ultrafiltration in Tubifex tubifex Müller (Annelida,Oligochaeta)

Summary The endothelia of Tubifex tubifex Müller consist of myoendothelial cells, chloragocytes, or podocytes. The latter seem to occur only as windows on the ventral vessel which has an endothelium of myoendothelial cells elsewhere. The podocytes are large cells, with several processes on the inner side which ramify into several pedicels. These are aligned upon the outside of the basement membrane which lines the inside of the endothelium. The gaps between adjacent pedicels are about 40 nm wide. In capillaries fenestrated endothelia occur with irregular spacings measuring up to 0.4–1 m. A diaphragm in podocytes or capillary fenestrations do not seem to exist. The basement membrane is the only continuous layer lining the blood vessels and capillaries of Tubifex with a rather uniform diameter in the range of 50 nm. It is the only permeability barrier between blood and coelomic fluid.     

Metabolic interlock between the acetolactate synthase isoenzymes and lysine biosynthesis in Escherichia coli K-12

Summary Some of the strains containing mutations in the genes for the acetolactate synthase isoenzymes are temperature sensitive (ts). Suppression of the acetolactate synthase defect due to one of these mutations suppresses also the ts phenotype; moreover, a genetic cross shows that the two phenotypes cannot be dissociated.The ts phenotype is accompanied by a decreased efficiency of transduction with Pl phage. Observations at the light microscope show formation of abnormal cells. Under specific conditions diaminopimelate stimulates growth and restores normal transduction efficiency. The rate of diaminopimelate formed and excreted by non-growing cells decreases when an acetolactate synthase mutation is present.We give evidence that the ts phenotype is due to an increased formation of lysine from diaminopimelate; this causes a starvation for the latter and therefore cell wall abnormalities. In fact, even at the permissive temperature, the lysine pool is 8x increased in a strain with an acetolactate synthase defect, while a slight decrease in the diaminopimelate pool is observed. Moreover, introduction into a ts strain of a mutation in lysA (the gene coding for diaminopimelate decarboxylase) cures the ts phenotype. Finally among the temperature resistant revertants we found some lysine auxotrophs.     

Isolation and visualisation of alkali stable protein/DNA complexes

Distinct polypeptides, 54,000–68,000 daltons in size, are alkali-stably bound to eukaryotic DNA. DNA fragments several hundred base pairs in length associated with these polypeptides are preferentially retained on glass fibre filters from solutions containing 1 M sodium chloride. About 50 percent of the protein/DNA complexes present in total DNA are retained on filters together with about 2 percent of the DNA. This preferential binding is demonstrated (a) by the ratio of ³H and ³⁵S radioactivity retained on filters after filtration of DNA from [³H]thymidine and L-[³⁵S]methionine labelled cells, (b) radioiodination of the material retained on filters and passing filters respectively and (c) by electron microscopical visualisation of the polypeptide component in the complexes after chemical modification with dinitrofluorobenzene (DNFB) followed by incubation with dinitrophenyl (DNP) specific antibodies.     

Utilization of limiting concentrations of ortho-phosphate and production of extracellular organic phosphates in cultures of marine diatoms

The utilization of ortho-phosphate by two coastal marine diatomspecies, Nitzschia closterium and Cyclotella cryptica, was studiedin batch cultures. The hypothesis was tested that thresholdconcentrations in the phosphate uptake determine the lower limitof environmental phosphate, permitting the existence of species.The turn-over time of residual medium phosphate in culturesis {small tilde}10 min, indicating a rapid equilibration ofconcentration dependent on uptake with leakage of ortho-phosphate.Increasing phosphate starvation in cultures diminished the residualortho-phosphate in the range of {small tilde}60–<2nmol l^–1, as measured radiochemically after elution onSephadex® G-10 gel. These concentrations encompass the rangeof limiting phosphate concentration in continuous cultures ofthe few microalgae, for which these concentrations are actuallymeasured. The diatoms excreted {small tilde}20–100 nmolI^–1 of organic phosphate. One dominating compound, probablyan unusual nucleotide, was incompletely or not resorbed underphosphate starvation. In contrast, Nitzschia closterium excretedunder ample phosphate supply a series of three related compounds,probably phospholipids, that were resorbed under depletion.The association of the organic phosphates with macromolecularexudates is interpreted, along with the other observations,as an indication for a hardly explored periplasmatic phosphatemetabolism in these algae. ³Dedicated to Prof. Dr. H.-A. von Stosch in honour of his 75thbirthday. ⁴This study was conducted at the University of Marburg undersupport of the Humboldt Foundation Publication no. 64 of theproject "Biological Research of the Eems-Dollard Estuary".     

Single amino acid substitutions in the B870 alpha and beta light-harvesting polypeptides of Rhodobacter capsulatus. Structural and spectral effects.

To obtain information on the structural and functional role of highly conserved amino acid residues in the B870 alpha and beta light-harvesting polypeptides of Rhodobacter capsulatus, site-directed mutagenesis was performed. 18 mutants with single amino acid substitutions at nine different positions in the B870 antenna polypeptides were prepared in a B800-850-lacking strain. The characterization of the resulting phenotypes was based on a quantification of the core-complex elements (reaction center, light-harvesting polypeptides, bacteriochlorophyll a and carotenoid) and the core-complex spectral characteristics (absorption maximum, absorption coefficient and fluorescence intensity). These data generally showed that strong structural effects were caused by the amino acid substitutions. Thus, the three tryptophan exchanges at the position alpha 8 resulted in either the absence of a core complex (alpha Trp8----Leu), the absence of the core antenna (alpha Trp8----Ala) or a reduction in the carotenoid content (alpha Trp8----Tyr). Likewise, the mutants alpha Pro13Gly (i.e. alpha Pro13----Gly), beta Gly10Val and alpha Phe23Ala demonstrated an abnormal protein/pigment ratio in the core antenna, while a drastically reduced antenna size resulted from the amino acid exchange beta Arg45Asp. In contrast to the structural effects, the absorption maxima and the fluorescence intensities of the mutant antennae differed only slightly from the wild type. The strongest blue shift of the bacteriochlorophyll a (8-11 nm) was induced by substitutions of the Trp at position alpha 43 (alpha Trp43----Ala, Leu or Tyr). Contrary to the other spectral effects, the absorption coefficient of bacteriochlorophyll a was strongly influenced by the amino acid substitutions and varied by 1.6-times less (beta Arg45Asp) and 1.3-times greater (alpha Phe25Ala) than normal. The antenna-free mutant, alpha Trp8Ala, yielded a high rate of B800-850 revertants during phototrophic growth, indicating a direct energy transfer from the B800-850 antenna to the reaction center in these strains. Although conditions for growth were generally observed to influence phenotypic expression, the structural as well as spectral effects were demonstrated to differ to the greatest extent between chemotrophically grown and phototrophically grown cells.     

The organization of the gene for the human cerebroside sulfate activator protein

The organization of 14 exons covering 97% of the cDNA sequence of human cerebroside sulfate activator protein precursor has been determined from two overlapping EMBL-4 human genomic clones extending over 17kb. All exons and exon/intron splice junctions and five introns were sequenced. Exon 8 consists of only 9 bp and is involved in alternative splicing which generates three different mRNAs of cerebroside sulfate activator precursor.     

Stimulation of human nitric oxide synthase by tetrahydrobiopterin and selective binding of the cofactor.

To check the stimulatory potency of the tetrahydro forms of the two major pteridines occurring in human tissues, neopterin and biopterin, NO synthase was purified 6000-fold from human cerebellum. Tetrahydrobiopterin stimulated the activity up to 4.5-fold in a concentration dependent manner with a maximum above 1 microM, whereas tetrahydroneopterin was completely inactive in concentrations up to 100 microM. Tetrahydrobiopterin, but not neopterin derivatives, were copurified with the NO synthase activity. Our results demonstrate that human cerebellum contains a tetrahydrobiopterin dependent NO synthase activity.