X-ray structure of recombinant horse L-chain apoferritin at 2.0 Å resolution: implications for stability and function

The X-ray structure of recombinant horse L-chain (rL) apoferritin, solved at 2.0?Å resolution with a final R factor of 17.9%, gives evidence that the residue at position 93 in the sequence is a proline and not a leucine, as found in earlier sequencing studies. The structure is isomorphous with other apoferritin structures, and we thus draw particular attention to those structural features which can be related to the stability and function of the protein. Analysis of hydrogen bonding and salt bridge interactions shows that dimers and tetramers are the most stable molecular entities within the protein shell: a result confirming earlier biophysical experiments. The stability of horse rL apoferritin to both dissociation into subunits at acidic pH values and to complete unfolding in guanidine chloride solutions is compared with that of other apoferritins. This emphasizes the role played by the salt bridge in the stability of this protein family. The horse rL apoferritin is significantly more resistant to denaturation than horse spleen ferritin, which in turn is more resistant than any human rH apoferritins, even those for which a salt bridge is restored. Finally, this structure determination not only establishes that a preformed pocket exists in L-chain apoferritin, at a site known to be able to bind porphyrin, but also underlines the particular function of a cluster of glutamic acids (E53, E56, E57 and E60) located at the entrance of this porphyrin-binding pocket.     

Induction of alternative oxidase synthesis by herbicides inhibiting branched-chain amino acid synthesis

Sycamore suspension cells ( Acer pseudoplatanus L.) were incubated in the presence of sulfonylurea and imidazolinone herbicides. These inhibitors of acetolactate synthase (ALS), a key enzyme of branched-chain amino acid synthesis, triggered a dramatic induction of the alternative oxidase (AOX). AOX activity increased in treated cells, eventually exceeding cytochrome (cyt) pathway activity. This induction of AOX activity was correlated with the accumulation of a 35 kDa AOX protein in isolated mitochondria, detected by Western blotting with a monoclonal antibody against Sauromatum guttatum AOX. It was preceded by the accumulation of putative 1.6 kb AOX mRNA, detected using an Aox cDNA probe from soybean. The metabolic perturbations induced by the herbicides rather than the herbicide molecules themselves were responsible for this induction of AOX. However, α-oxobutyrate (one of the substrates of ALS) and its transamination product, α-aminobutyrate, which accumulated after herbicide treatment, were not involved. The inhibition of branched-chain amino acid synthesis was probably somehow responsible for the AOX induction since: (i) a mixture of those amino acids (leucine, isoleucine, valine) prevented AOX induction by ALS inhibitors; (ii) the herbicide Hoe 704, a potent inhibitor of acetolactate reducto-isomerase (the enzyme following ALS in the branched-chain amino acid pathway), also triggered AOX induction.     

Auswirkungen von Hochspannungstrassen auf die Fl?chennutzung überwinternder Bl??- und Saatg?nseAnser albifrons, A. fabalis

Zusammenfassung  Während das Mortalitätsrisiko für Vögel durch Drahtanflug und Stromschlag an Hochspannungsleitungen vielfach untersucht wurde, könnte auch ein Einfluß von Hochspannungstrassen (110 kV) auf Vögel bestehen, die sich am Boden aufhalten. Dieser wurde 1994/95 am Beispiel der Flächennutzung überwinternder Bläß- und Saatgänse (Anser albifrons, A. fabalis) am Unteren Niederrhein untersucht. Da Gänse offene ungestörte Äsungsflächen beanspruchen, wurde der Arbeitshypothese nachgegangen, daß trassennahe Bereiche von Gänsen gemieden bzw. vermindert genutzt werden. Die Besuchsfrequenz von vier häufig genutzten trassenüberspannten Äsungsflächen wurde ermittelt. Im Anschluß an die einzelnen mehrtägigen Beäsungsphasen wurde die Losungsdichte (LD) als Maß der Flächennutzung senkrecht zum Trassenverlauf bestimmt. An 16–20 m hohen Trassen stieg die LD mit zunehmender Entfernung zur Trasse. Eine signifikante Abnahme der LD trat unterhalb von 40–80 m Abstand zur Trasse ein. Kleine Teilflächen, die durch die Trassen von größeren Bereichen abgetrennt sind, wurden weniger genutzt. An einer 60 m hohen, den Rhein Überquerenden Trasse, konnte kein trassenbedingter Unterschied der LD festgestellt werden. Mögliche Ursachen für die beschriebenen Effekte werden diskutiert.

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The impact of power lines on field selection and grazing intensity of wintering White-fronted- and Bean GeeseAnser albifrons, A. fabalis

In addition to studies about the mortality risk by collision and electrocution power lines may have an impact on birds during foraging behaviour on the ground. We examined this question in geese (Anser albfrons, A. fabalis) wintering in the lower Rhine area of North Rhine Westfalia (FRG) 1994/95. Because geese prefer large areas with low levels of disturbance by human activities or urbanic structures like buildings or roads, we hypothesized that they might be disturbed by the presence of power lines in their foraging sites and thus avoid areas next to the lines. To quantify the grazing intensity in relation to the distance from the power lines (110 kV), dropping densities have been repeatedly counted after independant grazing intervals in four different feeding sites. Our data show that: 1. Grazing intensity increases with the distance to power lines of low height. Significantly reduced grazing levels have been found in distances less than 80 to 40 m to the power lines. 2. No effects have been observed for a power line in an area next to the river rhine where the wires crossed the ground in a height of about 60 metres. 3. In small pasture or field areas, cut off by power lines from large ones, a generally reduced grazing amount is evident. Several conceivable reasons for the described effects are discussed.

     

DNA sequence analysis of mitochondrial Cyt-b and the species status ofLaniarius dubiosus (Rchw. 1899)

In 1899Reichenow described an african bushshrike in juvenile plumage as a new species. He named itLaniarius dubiosus. DNA from type material (feathers and skin) was extracted and DNA sequences from the mitochondrial Cyt-b gene were analysed. Comparisons of DNA-sequences from other bushshrikes (including the type-specimen from Luehder's bushshrikeLaniarius lühderi) support the judgement that dubiosus does not represent a full species rather than a representative of the western subspecies of the Luehder's bushshrikeLaniarius luehderi.

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Zusammenfassung Der vonReichenow (1899) als neue Art beschriebene, sich im Jugendkleid befindliche BuschwürgerLaniarius dubiosus ist nach DNA-Sequenzanalysen des mitochondrialen Cyt-b Genes mit hoher Wahrscheinlichkeit ein Jungvogel der westlichen Rasse des BraunscheitelwürgersLaniarius lühderi. Auf der Basis eines DNA-Stammbaumes von sieben verschiedenen Buschwürgern ist der 1991 neu beschriebeneLaniarius liberatus am wenigsten eng mitL. dubiosus verwandt.

     

Growth hormone/IGF-I and/or resistive exercise maintains myonuclear number in hindlimb unweighted muscles

Allen, David L., Jon K. Linderman, Roland R. Roy, Richard E. Grindeland, Venkat Mukku, and V. Reggie Edgerton. Growth hormone/IGF-I and/or resistive exercise maintains myonuclearnumber in hindlimb unweighted muscles. J. Appl.Physiol. 83(5): 1857-1861, 1997.In the presentstudy of rats, we examined the role, during 2 wk ofhindlimb suspension, of growth hormone/insulin-like growth factor I(GH/IGF-I) administration and/or brief bouts of resistance exercise in ameliorating the loss of myonuclei in fibers of the soleusmuscle that express type I myosin heavy chain. Hindlimb suspensionresulted in a significant decrease in mean soleus wet weight that wasattenuated either by exercise alone or by exercise plus GH/IGF-Itreatment but was not attenuated by hormonal treatment alone. Both meanmyonuclear number and mean fiber cross-sectional area (CSA) of fibersexpressing type I myosin heavy chain decreased after 2 wk of suspensioncompared with control (134 vs. 162 myonuclei/mm and 917 vs. 2,076 µm², respectively). NeitherGH/IGF-I treatment nor exercise alone affected myonuclear number orfiber CSA, but the combination of exercise and growth-factor treatmentattenuated the decrease in both variables. A significant correlationwas found between mean myonuclear number and mean CSA across allgroups. Thus GH/IGF-I administration and brief bouts of muscle loadinghad an interactive effect in attenuating the loss of myonuclei inducedby chronic unloading.

     

Recent approaches to probe functional groups in ribonuclease P RNA by modification interference

Modification interference is a powerful method to identify important functional groups in RNA molecules. We review here recent developments of techniques to screen for chemical modifications that interfere with (i) binding of(pre-)tRNA to bacterial RNase P RNA or (ii) pre-tRNA cleavage by this ribozyme. For example, two studies have analyzed positions at which a substitution of sulfur for thepro-Rp oxygen affects tRNA binding [1] or catalysis [2]. The results emphasize the functional key role of a central core element present in all known RNase P RNA subunits. The four sulfur substitutions identified in one study [2] to inhibit the catalytic step also interfered with binding of tRNA toE. coli RNase P RNA [1]. This suggests that losses in binding energy due to the modification at these positions affect the enzyme-substrate and the enzyme-transition state complex. In addition, the two studies have revealed, for the first time, sites of direct metal ion coordination in RNase P RNA. The potentials, limitations and interpretational ambiguities of modification interference experiments as well as factors influencing their outcome are discussed.Abbreviations nt nucleotide(s) - PAGE polyacrylamide gel electrophoresis     

Comparison of the main siderophores produced by some species of Streptomyces

The production of siderophores by four Streptomyces strains, S. ambofaciens, S. coelicolor, S. lividans, and S. viridosporus, was studied under iron-limited conditions. S. viridosporus produced two different siderophores: the linear desferrioxamine B and the cyclic desferrioxamine E. The latter was produced by the other strains and was the main siderophore of S. ambofaciens. The linear desferrioxamine G was the major form of S. coelicolor and S. lividans. The uptake rates of ⁵⁵Fe-labeled ferrioxamines by S. lividans and S. viridosporus showed that the G form was incorporated less efficiently than the B and E forms.     

Sperm motility in turbot,Scophthalmus marimus: initiation of movement and changes with time of swimming characteristics

Synopsis Turbot sperm motility is observed using dark field microscopy and stroboscopic illumination combined with video recording. Sperm motility is triggered by dilution of spermatozoa in sea water or in non ionic media (glucose or saccharose), presenting osmotic pressure ranging from 300 to 2100 mOsmol. The percentage of motile spermatozoa reaches 100% under conditions of osmotic pressure of 300 to 1100 mOsmol and pH close to 8.0. In full sea water, glucose or saccharose solutions an agglutination of spermatozoa is observed; this is prevented by addition of bovine serum albumin (5 mg ml^–1). Immediately after transfer in activation solutions, 100% spermatozoa are motile in most samples freshly stripped. This percentage drops suddenly between 15 and 30% after 70 to 100 sec. The beat frequency remains at a constant value of 50 Hz during 40 s post activation and then drops suddenly between 15 and 30 Hz. The spermatozoa velocity is about 200 micrometers s^–1 during 30 to 40 s and then declines to a stable value of 100 micrometers s^–1 at 50 s post activation. After 1.20 mn, more and more spermatozoa become motionless. The minimum calculated and averaged distance covered during 1.20 min, is about 12 mm. The high performances of turbot spermatozoa motility are interpreted as a compensatory mechanism for the low sperm production.     

Isolation of a YAC clone covering a cluster of nine S100 genes on human chromosome 1q21: rationale for a new nomenclature of the S100 calcium-binding protein family

S100 proteins are low-molecular-weight calcium-binding proteins of the EF-hand superfamily and appear to be involved in the regulation of a number of cellular processes such as cell cycle progression and differentiation. More than 10 members of the S100 protein family have been described from human sources so far. We have now isolated a YAC clone from human chromosome 1q21, on which 9 different genes coding for S100 calcium-binding proteins could be localized. Moreover, we have mapped the gene coding for S100P to human chromosome 4p16 and thereby completed the chromosomal assignments of all known human S100 genes. The clustered organization of S100 genes in the 1q21 region allows us to introduce a new logical nomenclature for these genes, which is based on the physical arrangement on the chromosome. The new nomenclature should facilitate and further the understanding of this protein family and be easily expandable to other species.