Alteration of ethanolamine glycerophospholipid turnover in trembler dysmyelinating mutant: An analysis of the sciatic nerve by biochemistry and radioautography

The turnover of phospholipids was compared in peripheral nerves of Trembler dysmelinating mutant and control mice, after intraperitoneal and local injection of labeled ethanolamine. In the mutant sciatic nerve, neurochemical analysis showed that [¹⁴C]ethanolamine is incorporated into EGP (ethanolamine glycerophospholipids) of the sciatic nerve at a much higher rate in Trembler mutant than in control mice. Furthermore the decay rate of ¹⁴C-labeled EGP is faster in Trembler than in normal animals. The accelerated turnover of EGP in Trembler sciatic nerve affects the diacyl-EGP while the renewal of the alkenylacyl-EGP (plasmalogens) is slower than in controls. Quantitative radioautographic study at the ultrastructural level corroborate that the initial increase of the label in Trembler nerve fibers was different in axons, Schwann cells and myelin sheaths. EM radioautographs reveal indeed that the high label content observed in Trembler axons takes place preferentially in the myelinated portions of axons and drops within 1 week. In both myelinated and unmyelinated segments of the axons, the majority of the radioactivity was contained in axolemma and smooth axoplasmic reticulum. The 10-fold increase of label found in the myelin sheath of Trembler nerve fibers at 1 day raises the question of the origin of the labeled EGP, either by a stimulated synthesis in Schwann cells or by transfer from axonally transported phospholipids. In contrast, the label of axons, Schwann cells and myelin sheaths of control nerve remains stable during the same period.     

Characterization of Tubulin in Mouse Brain Myelin

Analysis of mouse brain myelin by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that in the high-molecular-weight range it contained, besides the Wolfgram protein doublet, proteins comigrating with actin and with both subunits of tubulin. The occurrence of these alpha and beta subunits was confirmed by peptide mapping in myelin analyzed by two-dimensional electrophoresis. This tubulin did not arise from an artifactual binding of soluble brain tubulin to the myelin fraction: addition of exogenously labeled tubulin to brain homogenates proved that during myelin isolation by the procedure of Norton and Poduslo (1973) the contaminating tubulin was washed out. On the other hand, the distribution of tubulin isoforms in myelin was investigated by isoelectric focusing and compared with the distribution of the 21 isoforms listed for the whole brain soluble tubulin. It was shown that many isoforms were found in myelin (three isoforms for the alpha subunit and nine for the beta subunit), and that some isoforms were represented both in myelin and in soluble tubulin, but in different relative proportions.     

Donnees histologiques et ultrastructurales sur les organes lumineux du siphon de la pholade

Resumé Les organs photogènes de la pholade comprennent deux catégories de grandes cellules glandulaires.Les cellules lumineuses sécrètent une grande quantité de grains acidophiles, glyco ou mucoprotidiques, qui contiennent un glucide fortement Hotchkiss-positif et sont riches en tyrosine, en tryptophane et en protides sulfhydrilés. Certaines différences dans les affinités tinctoriales des grains s'expliquent en tenant compte de leur degré de maturité. Au terme de la phase d'élaboration du cycle sécrétoire, les derniers grains formés sont déversés dans la masse même du produit de sécrétion et le cytoplasme élaborateur, constitué surtout par de l'ergastoplasme et du réticulum endoplasmique lisse, subit une involution.Les cellules glandulaires apicales élaborent un mucus riche en mucopolysaccharides acides, dont l'ultrastructure est très particulière.Leur cycle sécrétoire semble, comme celui des cellules lumineuses, être caractérisé par la longueur exceptionnelle de la phase d'accumulation, ce qui a aussi pour conséquence une dégénérescence du cytoplasme élaborateur.Les cellules formant l'épithélium de revêtement de l'organe lumineux appartiennent à deux types distincts: les unes portent une abondante ciliature dont les battements favorisent sans doute le mélange des produits excrétés par les cellules glandulaires sous-jacentes. Les autres possèdent un ensemble de caractères qui permettent de les considérer comme des cellules glandulaires et il est possible qu'elles interviennent aussi lors de la réaction lumineuse.

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Summary The luminous organs of Pholas consist of two categories of large glandular cells, lying under a covering epithelium.The luminous cells secrete a great amount of acidophilic granules; these granules, of a glyco- or mucoprotidic nature, are rich in tyrosine, in tryptophan and in sulphydril groups; they contain also a glucid strongly PAS positive. Certain differences in the staining properties of the granules can be related to their degree of maturity. During the secretory cycle, at the end of the elaboration phase, the secretory product forms a mass into which the last granules to be formed are discharged. The cytoplasm, mainly made of rough and smooth endoplasmic reticulum, is at this stage degenerating.The apical glandular cells elaborate a mucus rich in acid mucopolysaccharides, the ultrastructure of which is very typical. The secretory cycle of these cells, as well as of the luminous cells, is characterized by the exceptional length of the accumulation phase, during which the cytoplasm degenerates.The cells of the covering epithelium are of two distinct types. Some bear numerous cilia, whose beating help to mix the secreted products of the large glandular cells. Others possess certain characteristics of glandular cells, and their possible implication in the luminous reaction should be considered.

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Je tiens à remercier le Dr. W. Bernhard pour son accueil dans le laboratoire de microscopie électronique de l'Institut du Cancer de Villejuif, où la partie ultrastructurale de ce travail a été effectuée. Ce travail a été exécuté dans le cadre d'une thèse de doctorat présentée devant la faculté des Sciences de Paris.     

Characterization of the Single Tyrosine Containing Troponin C from Lungfish White Muscle. Comparison with Several Fast Skeletal Muscle Troponin C's from Fish Species

Troponin C molecules from fast skeletal muscle of the following fish species (trout, whiting, lungfish, tilapia, and cod) have been purified to homogeneity. Upon binding of Ca²⁺ or Mg²⁺, lungfish troponin C is the only troponin C from fish white muscle to show the typical increase of tyrosine fluorescence emission quantum yield reported for rabbit fast skeletal muscle troponin C. The increase of tyrosine fluorescence signal occurring upon Ca²⁺ and Mg²⁺ titration of lungfish troponin C has been used to determine the corresponding affinity constants. With K_(Ca) = 7.0 10⁷ M⁻¹ and K_(Mg) = 3.6 10³ M⁻¹, the sites probed by the tyrosine residue of lungfish troponin C are typical of the COOH-terminal domain of fast skeletal troponin C's. The amino acid sequencing of the tyrosine containing tryptic peptides has allowed us to position the single tyrosine residue at position 7 in the Ca²⁺ binding loop of the third site, in identical position to Tyr109 of troponin C from rabbit fast skeletal muscle. Metal ion binding studies followed by intrinsic fluorescence or Tb³⁺ luminescence indicate that the conformation of the structural domain of lungfish troponin C with one metal ion bound is close to the physiological conformation of this domain.     

Identification of hemorphins in a cathepsin D bovine hemoglobin hydrolysate by radioimmunoassay and photodiode array detections

Summary Morphinomimetic peptides have been purified from hemoglobin enzymatic hydrolysates and a significant amount of evidence has been accumulated indicating that the generation of these peptides (hemorphins) might occur in vivo. In order to investigate their putative physiological role and processing from hemoglobin in vivo, two methods were developed: a specific radioimmunoassay and a UV spectra comparison analysis. These methods were applied to a cathepsin D bovine hemoglobin hydrolysate and allowed the detection of two hemorphin-7 peptides. This observation supports the putative implication of cathepsin D in the in vivo release of hemorphins. Among the two methods used in this study, the immunological approach exhibits higher sensitivity and represents a useful method to investigate the in vivo role and physiological processing of hemorphins.     

Darkness promotes flowering in the absolute long-day requiring plant, Lolium temulentum L. Ceres

Vegetative plants of the long-day grass Lolium temulentum L.Ceres were exposed to threshold long days or light breaks. Protracteddarkness given just afterwards clearly promoted flowering andwas weakly inductive on its own. The promotive effect of darknesswas restricted to floral induction since further apical developmentwas weak. Key words: Lolium temulentum, flowering, photoperiodism, darkness     

UV-inducible proteins and UV-induced cross-protection against acid,ethanol, H2O2 or heat treatments in Lactococcus lactis subsp. lactis

The relationship between UV-irradiation-induced tolerance to different environmental stresses and change in protein synthesis was examined in Lactococcus lactis subsp lactis IL1403. The results showed that preirradiation of cultures of L. lactis subsp. lactis with UV_254nm light led to increased tolerance of usually lethal challenges to acid (pH 4.0), ethanol (20%, v/v), H₂O₂ (15 mM), or heat (52° C). This suggests that there is an overlapping regulation between the UV-induced pathway and the other stress responses. Whole-cell protein extracts from UV-treated (100 J/m²) and untreated cultures were compared using two-dimensional polyacrylamide gel electrophoresis. At least 14 polypeptides were induced in response to damage after UV irradiation, which indicated an SOS-like response in this species. The RecA protein, however, seemed not to be significantly induced in Lactococcus lactis subsp. lactis IL1403. Some of the UV-induced polypeptides overlaped with stress proteins induced by the other treatments.     

AmpD, essential for both β-lactamase regulation and cell wall recycling, is a novel cytosolic N-acetylmuramyl-L-alanine amidase

In enterobacteria, the ampD gene encodes a cytosolic protein which acts as a negative regulator of β-lactamase expression. It is shown here that the AmpD protein is a novel N-acetylmuramyl-L-alanine amidase (E.C.3.5.1.28) participating in the intracellular recycling of peptido-glycan fragments. Surprisingly, AmpD exhibits an exclusive specificity for substrates containing anhydro muramic acid. This anhydro bond is mainly found in the peptidoglycan degradation products formed by the periplasmic lytic transglycosylases and thus might behave as a‘recycling tag’allowing the enzyme to distinguish these fragments from the newly synthesized peptidoglycan precursors. The AmpD substrate (or substrates) which accumulates in the absence of the corresponding enzymatic activity acts as an intracellular positive effector for β-lactamase expression and might represent an element of a communication network between the chromosome and the cell wall peptidoglycan.     

Ecdysone metabolism and endogenous moulting hormone titre during larval-pupal development in Choristoneura fumiferana

The titre and metabolism of ecdysone were studied in the last larval instar of the spruce budworm, Choristoneura fumiferana. Both in males and females a distinct ecdysone peak is present just before ecdysis. Injection of radioactive α-ecdysone into the insect when the endogenous level is low results in the transformation of most of the injected hormone into 3-dehydro-α-ecdysone and conjugates, with very little conversion to β-ecdysone. Whereas when the labelled material is administered when the endogenous level is high, the α-ecdysone is for the most part converted to β-ecdysone. The significance of the correlation between the endogenous titre of ecdysone and the metabolism of injected α-ecdysone is discussed.