NMR characterization of three forms of ferredoxin from Desulphovibrio gigas, a sulphate reducer

A NMR and magnetic susceptibility study of the oxidized and reduced states of three different oligomers (forms) of a [4Fe-4S] ferredoxin protein from Desulphovibrio gigas, FdI, FdI′, and FdII was carried out. FdI and FdI′ are different trimers and FdII a tetramer of the same basic subunit. A probable assignment of the contact shifted resonances is indicated. Since the temperature dependences of the contact shifted resonances associated with each [4Fe-4S] are not all similar a delocalized model for the spin densities on the 4Fe does not apply. The exchange rate between oxidized and reduced states is slow on the NMR time scale. The three oligomers are not magnetically equivalent. Using the “three state hypothesis” terminology it is shown that FdI_ox is predominantly in the C^2? state and changes upon reduction into the C^3? state, while FdII_ox is in the C^? state and changes into the C^2? state. FdI′ does not easily fit into this classification. This study shows a similarity of magnetic behaviour between FdI and bacterial ferredoxins (e.g. Bacillus polymyxa) and between FdII and HiPIP from Chromatium sp.. The influence of the quaternary structure on the stabilization of the different oxidation states of ferredoxins as well as on their redox potentials is discussed.     

Subcellular localization of tubulin in chick retina

Tubulin was measured through [3H]colchicine-binding in membrane and soluble components of chick retinal subcellular fractions. Total tubulin content was concentrated in the synaptosomal and rod outer segment fractions. Although in total retinal homogenate only 20% of total tubulin was associated to the membrane, in synaptosomes and photoreceptor outer segments, up to 50% of tubulin was bound to the membrane fraction. Results raise the possibility of tubulin participation in transmembrane phenomena which are common to transmitter release and photoexcitation.     

Evolution of the nucleotide sequence of influenza virus RNA segment 7 during drift of the H3N2 subtype

The complete genetic information contained in the influenza virus RNA segment 7 of the A/Bangkok/ $\text{1}\text{79}$ (H3N2) strain has been cloned by in vitro synthesis of the complementary dsDNA and its insertion into plasmid pBR322. The nucleotide sequence of the viral RNA segment has been determined from the cDNA insert. It is 1027 nucleotides long, and contains two open reading frames, as shown for other influenza virus strains. When compared with the previously published sequence for the A/Udorn/72 (H3N2) strain, 15 nucleotide exchanges are observed, most of them silent mutations, and only two causing amino acid changes in each of the M1 and M2 protein sequences.     

The effect of proteoglycans of cartilage and over-sulphated polysaccharides on the development of calcium-hydroxy-apatite (CHA) crystal formation in vitro

A coulometric model system is described which facilitates the quantitative study of the kinetics of transformation of amorphous calcium phosphate (ACP) into calcium-hydroxy-apatite (CHA) crystals. Proteoglycans of high molecular weight and over-sulphated polysaccharides (Arteparon, dextran sulphate) delayed CHA crystal formation. The results have enabled us to characterize the structure activity relationship of inhibitors of CHA formation, and to postulate a general structural requirement for molecules with inhibitory effect. As working mechanism, binding of calcium ions by sulphate groups of polyanions was supposed, which might reversibly impair "the critical nuclei formation", and/or further deposition of calcium ions in the CHA crystals. The clinical, therapeutical significance of the determination of the threshold concentration of different compounds is discussed.     

The effect of perinatal oestrogen treatment on the troph-hormone secreting cells of the anterior pituitary of the rat

Late effect of the perinatal administration of oestradiol dipropionate on pituitary gonadotrophs and the morphology of the LH-RH neuronal system was tested both in male and female rats. Oestrogen caused a severe reduction in the number and size of immunodetectable gonadotrophs in both sexes. By the 90th day of life, however, immunomorphology and distribution of the gonadotroph cells had became normal, and also the LH-RH system of the animals was similar to that of the intact controls. The lack of vaginal cycles indicated, however, that oestrogen might have permanently impaired higher brain centers regulating cyclic gonadotroph hormone release.     

Cytogenetics of the chinese giant salamander,Andrias davidianus (Blanchard): the evolutionary significance of cryptobranchoid karyotypes

Cytogenetic aspects of the cryptobranchid salamander Andrias davidianus of western China have been studied, including chromosome number and morphology, C-band patterns, meiosis, and the chromosomal localization of ribosomal 5S RNA genes. Our data regarding chromosome number (2n=60) and general chromosome morphology largely confirm the results of Morescalchi et al. (1977). The karyotype consists of 16 pairs of macrochromosomes that decrease gradually in relative length to 14 pairs of microchromosomes. Telocentric chromosomes are a conspicuous feature of the karyotype, representing more than half the genome. Differential staining reveals that all of the chromosomes, except four pairs of microchromosomes, have C-band heterochromatin in their centromeric regions, the amount varying irrespective of chromosome size. Faint bands of interstitial and telomeric C-band heterochromatin are found in mitotic chromosomes but are not seen in meiotic preparations. In C-banded mitotic preparations from a female, one of the smallest macrochromosome pairs is heteromorphic in respect to C-band heterochromatin and centromere position. In situ hybridization of an iodinated 5S RNA probe to meiotic chromosome preparations reveals that this repeated gene is clustered near the telomeric region of chromosome 7, a medium size telocentric, a location corresponding to a band of heterochromatin. Studies of spermatocytes indicate that the process of meiosis in A. davidianus closely resembles that of more advanced salamanders, and that the microchromosomes are meiotically stable. The significance of microchromosomes and chromosome morphology in the reorganization of salamander genomes during evolution is discussed on the basis of cytogenetic data available for A. davidianus and various other primitive and advanced salamanders.     

Urinary prostaglandin and kallikrein excretion are not flow dependent in the rat

To study the relationship between urine flow, urinary prostaglandin (PG) and kallikrein excretion in the rat high urine flow was induced in hydropenic Long-Evans rats by either hypotonic volume expansion or with manniitol or with furosemide. PGE, excretion remained unchanged during hypotonic volume expansion (134.5 ± 29.7 before and 153.0 ± 48.9 pg/min after) while it decreased significantly with mannitol (from 166.3 ± 32.4 to 45.2 ± 8.2 pg/min, p<0.01) and with furosemide (from 170.0 ± 20.4 to 29.5 ± 5.3 pg/min, p<0.001). PGF_2α excretion rates were slightly reduced following all three interventions. Urinary kallikrein excretion remained unchanged in all three groups of animals. It is concluded that, in contrast to human and dogs in the rat urine flow and urinary PG excretion are not interlinked.