Qualitative and quantitative observations on the structure of the Schwann cells in myelinated fibres

Various morphological features of the Schwann cells of myelinated fibres in the lizard thoracic spinal roots were studied, and, when possible, quantified using morphometric methods. About 0.8% of the Schwann cells are binucleate and some display clusters of microvilli along the internodes. The percentages of the cytoplasmic area of the Schwann cell occupied by the following cytoplasmic components were determined: mitochondria, Golgi apparatus, granular endoplasmic reticulum, smooth endoplasmic reticulum, multivesicular bodies, dense bodies, autophagic vacuoles, peroxisome-like bodies, lipofuscin granules and lipid droplets. Linear relationships were found between the sectional areas of the mitochondria and granular endoplasmic reticulum of the Schwann cell and both the length of the profile of the Schwann cell plasma membrane and the size of the related axon. The results obtained are compatible both with the hypothesis that the mitochondria and granular endoplasmic reticulum of the Schwann cell are involved in the production and storage of proteins for the plasma membrane of this cell, and with the hypothesis that these organelles are involved in the production and storage of protein metabolites which are subsequently transferred to the related axons.     

Molecular Cloning of the N-Terminus of GTBP

Defects in mismatch repair genes cause the genetic instability characteristic of hereditary nonpolyposis colorectal cancer and a subset of sporadic colon tumors. The newest member of the mismatch repair gene family,GTBP, has recently been identified as a partial cDNA. Here, we describe the isolation of its 5′ terminus, allowing definition of the entire coding region. Several polymorphisms within the 5′ end were identified and are presented.     

Intergenic spacers of rRNA genes in three species of theCynareae (Asteraceae)

Intergenic spacers of the rRNA genes of three species of theCynareae tribe:Cynara cardunculus subsp.scolymus (artichoke),Onopordum acanthium, andO. illyricum were cloned in the plasmid pGEM-7zf(+). Detailed restriction mapping and partial sequencing of the IGSs were carried out. The structural analysis showed a clear diversity betweenCynara andOnopordum, while a high degree of homology was found between the twoOnopordum spp. In all three species a fragment of about 450 bp from the 5 end of 18S to the Acc I site with a high sequence homology was present. Nucleotide sequences upstream from the above mentioned Acc I site show a gradual decrease of homology betweenCynara andOnopordum.     

The effect of light levels on daily patterns of chlorophyll fluorescence and organic acid accumulation in the tropical CAM treeClusia hilariana

Sandy plains are characteristic of the coastal region of Brazil. We investigated the diel patterns of changes in organic acid levels, leaf conductance and chlorophylla fluorescence for sun-exposed and shaded plants ofClusia hilariana, one of the dominant woody species in the sandy coastal plains of northern Rio de Janeiro state. Both exposed and shaded plants showed a typical CAM pattern with considerable diel oscillations in organic acid levels. The degradation of both malic and citric acids during the midday stomatal closure period could lead to potential CO₂ fixation rates of 28 mol m^-2 s^-1 in exposed leaves. Moreover, exposed leaves exhibited large increases in total non-photochemical quenching (q_N) accompanied by a substantial decrease in effective quantum yield during the course of the day. However, these potential high rates of CO₂ fixation and the increases inqn of exposed plants were not enough to maintain the primary electron acceptor of photosystem II (q_A) in a low reduction state, similar to that of shaded plants. As a result, there was a moderate increase in the reduction state of q_A throughout the day. Most of the decline in photochemical efficiency of exposed leaves ofC. hilariana was reversible, as evidenced by the high levels of pre-dawn potential quantum yields (F_v/F_m) and their rapid recovery after sunset. However, the depletion of the organic acid pool in the afternoon resulted in an accentuated subsequent drop in F_v/F_m, suggesting that prolonged periods of water stress accompanied by high irradiance levels may expose plants ofC. hilariana in unprotected habitats to the danger of photoinhibition.     

Cyclodextrins enhance the aerobic degradation and dechlorination of low-chlorinated biphenyls

Summary The aerobic dechlorination of 4-chlorobiphenyl and of Aroclor 1221 by Pseudomonas sp. CPE1 strain was enhanced by the presence of hydroxypropyl--cyclodextrin in the medium. The best dechlorination results were obtained when 4-chlorobiphenyl or Aroclor 1221 and the cyclodextrin were used at the molar ratios 1:1 and 1:1.5. This agent can be adopted to enhance the efficiency of PCB degradation tests.     

Synthesis and biological evaluation of novel NK-1 tachykinin receptor antagonists: The use of cycloalkyl amino acids as a template

In the course of a program aimed at synthesizing novel, potent NK-1 tachykinin receptor antagonists, we developed upon a bioactive model by comparing the low energy structures of a series of peptide and nonpeptide Substance P antagonists. The comparison was based on the super imposition of the aromatic rings, assuming that the rest of the molecule behaves predominantly as a template to arrange the key aromatic groups in the right spatial position. A series of 2-aminocyclohexane carboxylic acid analogues were then selected as the best templates for reproducing the postulated bioactive structure, leading to several pseudo-peptides with interesting biological activity. According to the molecular modeling, these compounds exhibit a neat parallel facing of the indolyl and naphthyl groups at about 3 Å distance. Ultraviolet absorption and steady state fluorescence measurements support this conclusion, showing a linear correlation between the spectral properties and the binding affinity of these analogues. Stacking of the indole ring with naphthalene gives rise to a complex characterized by a well-defined molar extinction coefficient. Consistently, steady state and lifetime fluorescence measurements suggest that the quenching process is ascribable to ground-state interactions between the chromophores. Implications of the π stacking propensity of aromatic groups in the biological activity of the compounds examined are briefly discussed. © 1995 John Wiley & Sons, Inc.     

Expression of {beta}-galactoside {alpha}2,6-sialyltransferase does not alter the susceptibility of human colon cancer cells to NK-mediated cell lysis

The extent of processing of N-linked oligosaccharides and thesialylation of the target cell membranes has been positivelycorrelated with resistance to lysis mediated by NK cells, buta conclusive evidence has never been reached. Colon cancer tissuesexpress an increased activity of ß-ga-lactoside     

In vivo replication of carcinogen-modified rat liver DNA: increased susceptibility of O6-methylguanine compared to N-7-methylguanine in replicated DNA to S1-nuclease

In order to characterize rat liver DNA replicated $\text{in}\text{vivo}$ on a carcinogen-damaged template, the replicated DNA was treated with S₁-nuclease and the release of (¹⁴C)-dimethyl-nitrosamine induced 0⁶-methylguanine, a lesion associated with miscoding and N-7-methylguanine, a lesion that does not miscode were monitored. The results indicated that both the methylated guanines became susceptible to S₁-nuclease upon replication. However, a greater percentage of 0⁶-methylguanine (22% of the total 0⁶-methylguanine present in the DNA) compared to N-7-methylguanine (4% of the total N-7-methylguanine present in the DNA) was rendered acid soluble by S₁-nuclease. The preferential release of 0⁶-methylguanine compared to N-7-methylguanine from replicated DNA was interpreted to indicate its occurrence in local denatured regions probably generated as a result of misbase pairing.     

Structural investigation of the capsular polysaccharide of klebsiella serotype K26

The structure of the capsular polysaccharide from Klebsiella K26 has been determined by using the techniques of methylation, periodate oxidation, partial hydrolysis, and β-elimination. N.m.r. spectroscopy (¹H and ¹³C) was used to establish the nature of the anomeric linkages and to identify oligosaccharides obtained by the different degradative techniques employed.The polysaccharide is comprised of repeating units of the heptasaccharide shown.