A new species of Lernanthropus De Blainville, 1822 (Copepoda: Lernanthropidae) parasitic on Menticirrhus ophicephalus (Jenyns) (Teleostei: Sciaenidae) from the Peruvian coast

Lernanthropus huamani n. sp. (Copepoda: Lernanthropidae), a parasite of the Peruvian sciaenid fish Menticirrhus ophicephalus (Jenyns), is described and illustrated. The new species differs from all other species of Lernanthropus by a combination of characters, including the dorsal plate, legs and other appendages. L. guacoldae Villalba & Fernández, 1984 is considered a synonym of L. pacificus Oliva & Duran, 1982.     

Neuromuscular development following tetrodotoxin-induced inactivity in mouse embryos

Developmental aspects of the neuromuscular system in mouse embryos chronically paralyzed in utero with tetrodotoxin (TTX) between embryonic days 14 and 18 were studied using biochemical and histological methods. The number of lumbar spinal motoneurons (MNs) was higher in inactive embryos than in controls suggesting a decreased motoneuron cell death. In association with the increase in MN number, choline acetyltransferase activity was significantly increased in both spinal cord and peripheral synaptic sites. Paralyzed muscles exhibited a decreased number of mature myofibers and the nuclei were centrally located. Creatine kinase activity was greatly decreased and total acetylcholine receptor and receptor cluster numbers per myofiber were significantly increased in paralyzed muscles. A similar pattern of changes occurs in the neuromuscular system of the mutant mouse muscular dysgenesis (mdg). However, in contrast to the mdg mutant, tetrodotoxin-treated muscles were similar to controls in their innervation pattern, in the ultrastructural aspects of the excitation–contraction coupling system (i.e., dyads and triads) and in the extent of dihydropyridine binding. Thus, neuromuscular inactivity is not sufficient to impair the pattern of muscle innervation or the appearance of either the triadic junctions or dihydropyridine receptors. These results indicate that alterations of dihydropyridine binding sites and triads in muscular dysgenesis cannot be accounted for by inactivity but rather must reflect a more primary defect involving the structural gene(s) regulating the development of one or more aspects of muscle differentiation.     

Involvement of the Dihydropyridine Receptor and Internal CaStores in Myoblast Fusion

The process of myoblast fusion during skeletal myogenesis is calcium regulated. Both dihydropyridine receptor and ryanodine receptor are already present on muscle precursors, at the prefusional stage, before they are required for excitation–contraction coupling. Previous pharmacological studies have shown the need for a special pool of Ca²⁺associated with the membrane for the fusion process to occur. We hypothesized that this pool of Ca²⁺is mobilized via a machinery similar to that involved in excitation–contraction coupling. The process of fusion in rat L6 muscle precursors was either totally or partially abolished in the presence of the L-type calcium channel inhibitors SR33557 and nifedipine (half inhibition towards 2 μM), respectively. The inhibition was reversible and dose-dependent. Drugs able to deplete internal calcium stores (caffeine, ryanodine, and thapsigargin) were also tested on the fusion. Both caffeine and thapsigargin drastically inhibited fusion whereas ryanodine had no effect. This suggests that fusion may be controlled by internal pools of Ca²⁺but that its regulation may be insensitive to ryanodine. We presumed that an early form of the ryanodine receptor may exist, with different pharmacological properties than the adult forms. Indeed, Western blot analysis of pre- and postfusional L6 cells demonstrated the presence, at the prefusional stage, of a transient form of the ryanodine receptor protein with an apparent molecular weight slightly different from those of the classical skeletal and cardiac forms. Taken together, these results support the hypothesis that the fusion process is driven by a mechanism involving both the dihydropyridine receptor (α1 subunit of the L-type Ca²⁺channel) and the internal stores of Ca²⁺. The machinery underlying this mechanism might consist of slightly different forms of the classic molecules that in adult muscle ensure excitation–contraction coupling. It remains to be seen, however, whether the mobilization of the internal pool of Ca²⁺is triggered by the type of mechanism already described in skeletal muscle.     

Analysis of inbreeding in a colonizing population of Drosophila subobscura

An analysis of the effects of inbreeding on the genetic structure of a colonizing population of Drosophila subobscura has been carried out. Species of Drosophila, particularly D. subobscura, may have lethal alleles associated with chromosomal inversions and our aim was to assess the extent to which the genome is balanced in this way. The frequencies of chromosomal inversions were compared between a large population and a set of 72 lines that were maintained by brother-sister mating for 10 generations. Fisher's matrix method was used to calculate the expected homozygosity in these inbred lines for 5 allozyme loci (Aph, Hk-1, Lap, Odh, and Pept-1) used as markers of large chromosomal segments. Furthermore, the expected rates of fixation corresponding to these allozyme loci were also calculated. The results show that the amount of homozygosis observed did not differ significantly from expectations (with the corresponding loss of lines as a consequence of the reduction in viability). However, two deviations from strict neutrality were observed: there was a heterozygote excess at the Lap locus, and the frequency of the O ₅ inversion (always associated with a lethal gene in colonizing populations) was higher than expected.     

Trinuclear iridium and rhodium complexes: the solution to a puzzle involving the multiple coordination possibilities of 1,8-naphthyridine-2-one ligands

The multiple coordination possibilities of 1,8-naphthyridine-2-one (HOnapy) and 5,7-dimethyl-1,8-napthyridine-2-one (HOMe₂napy) ligands allow the synthesis of a variety of tri- di- and mononuclear complexes, showing fluxional behaviour and frequent exchange of the coordinated ML₂ fragments. Thus, reactions of [M₂(μ-OMe)₂(cod)₂] (cod = 1,5-cyclooctadiene) with HOnapy and HOMe₂napy yield the compounds of the general formula [M(μ-OR₂napy) (cod)]_n (M = Ir, R = Me (1a, 1b, H (2); M = Rh, R = Me (3a, 3b). They crystallise as inconvertible yellow (a) and purple/orange (b) forms and also show a puzzling behaviour in solution. X-ray diffraction studies on both forms (3a, 3b) and spectroscopic data reveal that the yellow forms are mononuclear complexes whilst the dark-coloured crystals contain dinuclear complexes. In solution, the nuclearity of the complexes depends on the solvent. In addition both types of complexes are fluxional. The mixed-ligand complexes [M₂(μ-OMe₂napy)₂(CO)₂(cod)] M = Ir (5), Rh (6) have been isolated and characterised; they are found to be intermediates in the synthesis of the trinuclear complexes [M₃(μ₃-OMe₂napy)₂(CO)₂(cod)₂]⁺ M = Rh (8), Ir (9). Reactions of [IrCl(CO)₂(NH₂-p-tolyl] with the complexes [Rh(μ-OR₂napy)(diolefin)]_n followed by addition of a poor donor anion is a general one-pot synthesis for the hetertrinuclear complexes [Rh₂Ir(μ₃-OR₂napy)₂(CO)₂(diolefin)₂]⁺ (R=Me, DIOLEFIN = cod (10), tetrafluorobenzo-barrelene (tfbb) (11), 2,5-norbornadiene (nbd) (12); R=H, DIOLEFIN=cod (13)). This synthesis follows a stepwise mechanism from the mononuclear to the trinuclear complexes in which mixed-ligand heterodinuclear complexes are involved as intermediates of the type [(diolefin)Rh(μ-OMe₂napy)₂Ir(CO)₂]. Heteronuclear complexes which possess the core [RhIr₂]³⁺, such as [RhIr₂(μ₃-OR₂napy)₂(CO)₂(cod)₂]BF₄ (R=Me (14), H (15)), result from the reaction of 1 or 2 with [Rh(CO)₂S_x]⁺ (S = solvent). The trinuclear complexes undergo two chemically reversible one-electron oxidation processes. The chemical oxidation of 10, 14 and 9 with silver salts gives the mixed-valence trinuclear radicals [Rh₂Ir(μ₃-OMe₂napy)₂(CO)₂(cod)₂]²⁺ (16), [RhIr₂(μ₃-OMe₂napy)₂(CO)₂(cod)₂]²⁺ (17) and [Ir₃(μ₃-OMe₂napy)₂(CO)₂(cod)₂]²⁺ (18), which have been isolated as the perchlorate and tetrafluoroborate salts. The EPR spectrum of 16 indicates that the unpaired electron is essentially in an orbital delocalised on the metals. The molecular structures of the complexes 3a, 3b, 6, 10b and 16a are described. Crystals of 3a are triclinic, P-1, with a = 9.7393(2), b = 14.0148(4), c = 16.0607(4) Å, α = 88.122(3), β = 83.924(3), γ = 87.038(3)°, Z = 4; 3b crystallises in the Pna2_i orthorhhombic space group, with a = 16.7541(3), B = 11.7500(8), c = 17.7508(7) Å, Z = 4; complex 6 is packed in the monoclinic space group P2_i/c, a = 9.6371(1), b = 11.8054(4), c = 27.2010(9) Å, β = 90.556(4)°, Z = 4; crystals of 10b are monoclinic, P2₁/n, with a = 17.546(7), b = 13.232(6), c = 17.437(8) Å, β = 106.18(1)°, Z = 4; crystals of 16a are triclinic, P-1, with a = 10.318(4), b = 12.562(6), C = 19.308(8) Å, α = 92.12(8), β = 97.65(9), γ = 90.68(5)°, Z = 2. The five different structures show the coordination versatility of the OMe₂napy molecule as ligand, which behaves as a N,N′-chelating (3a), bidentate N,O-donor (3b, 6), or as a tridentate N,N′,O-donor bridging ligand (10b, 16a).     

Identification of two glutaminases inRhizobium etli

We present evidence thatRhizobium etli has two glutaminases differentiated by their thermostability and electrophoretic mobility. The thermostable glutaminase (B) is constitutive, in contrast with the thermolabile glutaminase (A), which is positively regulated by glutamine and negatively regulated by ammonium and by the carbon source. In distinction to glutaminase A, glutaminase B plays a minor role in the utilization of glutamine as a carbon source, but it may play a role in maintaining the balance of glutamine and glutamate. By complementation of theRhizobium etli LM16 mutant that lacks glutaminase A, we have cloned the gene that codes for this enzyme.     

Water potentials for developing cladodes and fruits of a succulent plant, including xylem-versus-phloem implications for water movement

Developing cladodes had lower water potentials and developingfruits had higher water potentials than the underlying cladodesof the widely cultivated prickly pear cactus, Opuntia ficus-indica.The 0.06 MPa lower value in 4-week-old daughter cladodes indicateda typical water potential gradient from the underlying clad-odealong the xylem of –0.2 MPa m^–1; the 0.17 MPa highervalue in 4-week-old fruits, which decreased to 0.07 MPa by 10weeks, implicated the phloem as their supplier of water. Thephloem sap of the underlying cladodes had an osmotic pressureof only 0.90 to 0.98 MPa, so the phloem could supply a relativelydilute solution to the photosynthetically dependent fruits (daughtercladodes of O. ficus-indica are photosynthetically independentat 4 weeks). Although the water potentials were similar foradjacent tissues, the osmotic pressures were lower for the water-storagecompared with the photosynthetic tissue; the osmotic pressureswere higher for xylem sap from fruits, for which xylary flowapparently occurred toward the underlying cladodes, than fordaughter cladodes. The relative capacitance (change in relativewater content divided by change in tissue water potential) wasapproximately 0.71 MPa^–1 for the water-storage tissueand the photosynthetic tissue of both daughter cladodes andfruits at 4 weeks of age. When these organs approached maturityat 10 weeks, the relative capacitance increased about 40% fortheir water-storage tissue, but decreased 30% for their photosynthetictissue. As the plant water content decreases during drought,about twice as much water will thus be lost per unit volumeof the water-storage tissue compared with the photosynthetictissue of maturing fruits and cladodes. Key words: Opuntia ficus-indica, phloem, relative water content, water capacitance, water potential     

Redox-active bis-cysteinyl peptides. II. Comparative study on the sequence-dependent tendency for disulfide loop formation

Bis (cysteinyl) octapeptides related to the active sites of the oxidoreductases protein disulfide isomerase (PDI), thioredoxin reductase (trr), glutaredoxin (grx), and thioredoxin (trx) were analyzed for their propensity to form the intramolecular 14-membered disulfide ring in oxidation experiments. The rank order of percentage of cyclic monomer formed in aqueous buffer (pH 7.0) at 10^?3 M concentration was found to be very similar, but opposite to that of the K_ox and, correspondingly, of the redox potentials of the native enzymes. Attempts to induce intrinsic conformational preferences of the peptides by addition of trifluoroethanol led to enhancements of β-turn structures as reflected by the CD and Fourier transform ir spectra. The induced secondary structure, instead of aligning the tendencies of the excised fragments for loop formation with those of the intact proteins, was found to suppress the differences by significantly increasing the preference for cyclic monomers (≈ 90%). Similarly, operating under denaturing conditions, i.e., in 6M guanidinium hydrochloride, only for the trx peptide was the statistical product distribution obtained. For the remaining peptides, again a strong increase of cyclic monomer contents was observed that could not be correlated with dissolution of β-sheet type aggregates. The CD spectra are more consistent with the presence of ordered structure to some extent, possibly resulting from an hydrophobic collapse of the sparingly soluble peptides. The results of the oxidation experiments further support previous findings from thiol disulfide interchange equilibria, which clearly revealed a decisive role of the characteristic thioredoxin structural motif in dictating the redox properties of the enzymes. Point mutations in the active sites of the oxidoreductases allowed us to affect their redox potentials strongly, but apparently only in the constraint form of the three-dimensional structure as similar exchanges in the excised fragments did not produce the expected effect. This observation contrasts with numerous reports that the conformation of short disulfide loops is mainly dictated by the amino acid sequence. © 1994 John Wiley & Sons, Inc. © 1994 John Wiley & Sons, Inc.