Mature ferredoxin-NADP reductase with a glutaminyl residue at N-terminus from spinach chloroplasts

When 35%-acetone extract of spinach chloroplasts was separated by SDS-PAGE, ferredoxin-NADP reductase (FNR) appeared as a single band at a molecular mass of 35 kDa. After the polypeptides on the SDS-PAGE plate were electroblotted onto PVDF membrane, the FNR band was cut out and analyzed for N-terminal structure in a gas-phase protein sequencer. Two different FNR peptides were identified: one with glutamine at its N-terminus (Gln-FNR) and the other with -pyroglutamic acid (tFNR) fraction was extracted from chloroplasts with their loosely bound FNR (lFNR) fraction removed in advance. The tFNR fraction contained Gln-FNR only. The Gln-FNR could be highly purified by affinity chromatography using a ferredoxin column. The purified Gln-FNR was digested with arginyl endopeptidase for peptide mapping and partial sequence analysis. Primary structure of Gln-FNR differed from that of lFNR loosely bound FNR - tFNR tightly bound FNR - -pyroglutamic acid at N-terminus     

Fatty acid composition of vitellogenin from four teleost species

The fatty acid compositions of vitellogenin and liver from cod (Gadus morhua), rainbow trout (Oncorhynchus mykiss), turbot (Scophthalmus maximus) and wolffish (Anarhichas lupus) were determined. Vitellogenin was isolated from plasma of estradiol-17-treated fish by precipitation with EDTA-Mg²⁺ and distilled water or by high-performance ion-exchange chromatography. In all investigated species, vitellogenin contained 16–18% (w/w) lipid, in which polyunsaturated fatty acids, predominantly 20:5 (n-3) and 22:6 (n-3), comprised about 50% of the total fatty acids. The proportions of saturated, monounsaturated, polyunsaturated and (n-3) fatty acids in vitellogenin of the different species were generally similar, although the relative content of specific fatty acids was distinctive for each species. The distribution of fatty acids in total lipids of vitellogenin was highly consistent among individual females of each species. In contrast, liver fatty acid composition varied considerably, both within and between species. Altogether, the differences in the fatty acid composition of vitellogenin and liver from each species indicate that a specific selection of fatty acids occurs during the lipidation of vitellogenin.Abbreviations BHT butylated hydroxytoluene - E-17 estradiol-17 - EDTA ethylenedinitrilo tetra-acetic acid disodium salt dihydrate - FA fatty acids - FAME fatty acid methyl esters - HDL high density lipoproteins - PUFA polyunsaturated fatty acids - SD standard deviation - TLC thin-layer chromatography - VHDL very high density lipoproteins - VLDL very low density lipoproteins - v/v volume per volume - w/v weight per volume - w/w weight per weight     

In vitro investigation of α-amylase release from the digestive cells of the bivalve mollusc Pecten maximus: effect of second messengers and biogenic amines

The (neuro)endocrine control of enzyme release from invertebrate digestive cells remains poorly understood. A tissue dissociation procedure was developed to investigate the regulatory mechanisms of -amylase discharge from the cells of the stomach-digestive gland complex of the scallop Pecten maximus. The validity of the experimental system was tested by increasing the intracellular concentration of second messenger analogues (N ⁶,2-o-dibutyryl-adenosine-3,5 cyclic monophosphate and the ionophore A23187) known to mimic the activity of naturally occurring secretagogues in vertebrates: N ⁶,2-o-dibutyryl-adenosine-3,5 cyclic monophosphate increased the time and dose-dependent release of -amylase in a similar way as in vertebrates. A23187 was also very effective in inducing enzyme discharge. Since the in vitro bioassay was shown to be functional and because axon terminals were previously seen in close contact to -amylase secreting cells, the effect of some classic neurotransmitters was explored. Only the cholinergic agonist carbachol and dopamine evoked a secretory response. Maximal stimulation of -amylase release was reached at 10^-5 mol·l^-1 carbachol; at the same concentration dopamine was less effective than carbachol. By contrast, serotonin was totally inactive. The in vitro bioassay should prove useful for the identification of regulatory molecules involved in the control of enzyme discharge and to study stimulus secretion coupling mechanisms in scallop digestive cells.Abbreviations DBcAMP N ⁶, 2-O-dibutyryl-adenosine-3,5 cyclic monophosphate - cAMP adenosine-3,5 cyclic monophosphate     

Molecular phylogeny based on the κ-casein and cytochrome b sequences in the mammalian suborder Ruminantia

Nucleotide sequences for the -casein precursor proteins have been determined from the genomic DNAs or hair roots of the Ruminantia. The coding regions, exons 2, 3, and 4, were amplified separately via the three kinds of PCRs and then directly sequenced. The primers were designed from the sequence of bovine -casein gene; they were applicable for the amplification of the -casein genes from the 13 species in the Ruminantia except exon 2 of the lesser mouse deer. These results permitted an easy phylogenetic analysis based on the sequences of an autosomal gene. A phylogenetic tree was constructed from the mature K-casein sequences and compared with the tree of the cytochrome b genes which were sequenced from the same individuals. The Cervidae (sika deer, Cervus nippon) were separated from the branch of the Bovidae on the tree of -casein genes with a relatively high confidence level of the bootstrap analysis, but included in the branch of the Bovidae on the tree of cytochrome b genes. The -casein tree indicated a monophyly of the subfamily Caprinae, although the internal branches were uncertain in the Caprinae. The tree based on the nucleotide sequences of cytochrome b genes clearly showed the relationships of the closely related species in the genus Capricornis consisting of serow (C. smatorensis), Japanese serow (C. crispus), and Formosan serow (C. swinhoei). These results would be explained by the difference of resolving power between the -casein and the cytochrome b sequences. Correspondence to: K. Chikuni     

Presence and abundance of CENP-B box sequences in great ape subsets of primate-specific α-satellite DNA

CENP-B, a highly conserved centromere-associated protein, binds to -satellite DNA, the centromeric satellite of primate chromosomes, at a 17-bp sequence, the CENP-B box. By fluorescence in situ hybridization (FISH) with an oligomer specific for the CENP-B box sequence, we have demonstrated the abundance of CENP-B boxes on all chromosomes (except the Y) of humans, chimpanzee, pygmy chimpanzee, gorilla, and orangutan. This sequence motif was not detected in the genomes of other primates, including gibbons, Old and New World monkeys, and prosimians. Our results indicate that the CENP-B box containing subtype of -satellite DNA may have emerged recently in the evolution of the large-bodied hominoids, after divergence of the phylogenetic lines leading to gibbons and apes; the box is thus on the order of 15–25 million years of age. The rapid process of dispersal and fixation of the CENP-B box sequence throughout the human and great ape genomes is thought to be a consequence of concerted evolution of -satellite subsets on both homologous and nonhomologous chromosomes.Correspondence to: T. Haaf     

Yeast Kre1p is a cell surface O-glycoprotein

The Saccharomyces cerevisiae KRE1 gene encodes a secretory protein required for the production of the cell wall polymer (1 6)--glucan. Here we report further characterization of the KRE1 gene product, Krelp. A functional, epitope-tagged Krelp is shown to be highly modified in a SEC53-dependent manner. Krelp is O-glycosylated, but the basis for the majority of its post-translational modification is unknown. Fractionation of Kre1p reveals a cell wall-associated form and a less abundant membrane-associated species. Indirect immunoflurorescence demonstrates that Kre1p localizes to the cell surface, where it becomes concentrated at the surface of mother cells. Such a localization of Kre1p seems to parallel the CAL1/CSD2-dependent cell wall deposition of chitin found in S. cerevisiae, and is consistent with evidence from Schizophyllum commune that (1 6)--glucan accumulates during maturation of the subapical region of the wall distal to the hyphal tip.     

Analysis of the loop-helix interaction in bundle motif protein structures

Molecular dynamics simulations and energy analysis have been carried out to study the structural mobility and stability of the four -helix bundle motifs. The simulation results as well as the X-ray data show that the atomic RMS fluctuation is larger at the loop region for four representative proteins investigated: methemerythrin, cytochrome b-562, cytochrome c, and bovine somatotropin. The loop-loop, helix-helix, and loop-helix interactions are computed for the unfolded and folded proteins. In the folded and solvated protein structures the loop-helix interaction is stronger than the helix-helix interaction, especially in the electrostatic component. But the stabilization energies of both the loop-helix and the helix-helix interactions relative to the those of an unfolded structure are of the same order of magnitude. The stabilization due to protein-solvent interaction is greater in the helix region than in the loop region. The percentage of hydrophilic solvent accessible area for the four proteins studied was calculated with the method of Eisenberg and McLachlan. The percentage of the hydrophilic area is greater in the loops than in the helices. A Poisson-Boltzmann calculation shows that the potential from the loops acting on a helix is generally more negative than that from other helices.     

Glutamine metabolism in AS-30D hepatoma cells. Evidence for its conversion into lipids via reductive carboxylation

A study was undertaken to assess the role of a physiological concentration of glutamine in AS-30D cell metabolism. Flux of¹⁴C-glutamine to¹⁴CO₂ and of¹⁴C-acetate to glutamate was detected indicating reversible flux between glutamate and TCA cycle -ketoglutarate. These fluxes were transaminase dependent. A flux analysis was compared using data from three tracers that label -ketoglutarate carbon 5, [2-¹⁴C]glucose, [1-¹⁴C]acetate and [5-¹⁴C]glutamine. The analysis indicated that the probability of flux of TCA cycle -ketoglutarate to glutamate was, at minimum, only slightly less than the probability of flux of -ketoglutarate through -ketoglutarate dehydrogenase. The apparent Km for oxidative flux of [¹⁴C]glutamine to¹⁴CO₂, 0.07 mM, indicated that this flux was at a maximal rate at physiological, 0.75 mM, glutamine. Although oxidative flux through -ketoglutarate dehydrogenase was the major fate of glutamine, flux of glutamine to lipid via reductive carboxylation of -ketoglutarate was demonstrated by measuring incorporation of [5-¹⁴C]glutamine into¹⁴C-lipid. In media containing glucose (6 mM), and glutamine (0.75 mM) 47 per cent of the lipid synthesized from substrates in the media was derived from glutamine via reductive carboxylation and 49 per cent from glucose. These findings of nearly equal fluxes suggest that lipogenesis via reductive carboxylation may be an important role of glutamine in hepatoma cells.     

Bifurcation, Bursting, and Spike Frequency Adaptation

Many neural systems display adaptive properties that occur on timescales that are slower than the time scales associated withrepetitive firing of action potentials or bursting oscillations. Spike frequency adaptation is the name givento processes thatreduce the frequency of rhythmic tonic firing of action potentials,sometimes leading to the termination of spiking and the cell becomingquiescent. This article examines these processes mathematically,within the context of singularly perturbed dynamical systems.We place emphasis on the lengths of successive interspikeintervals during adaptation. Two different bifurcation mechanisms insingularly perturbed systems that correspond to the termination offiring are distinguished by the rate at which interspike intervalsslow near the termination of firing. We compare theoreticalpredictions to measurement of spike frequency adaptation in a modelof the LP cell of the lobster stomatogastric ganglion.