The influence of cytidine on the endogenous pool of CDP-choline,CDP-ethanolamine,and CMP of the rat brain

Cold cytidine was intraventricularly administered into the brain of young rats, and its effect on CDP-choline, CDP-ethanolamine, and CMP pools followed for different time intervals and with various amounts of administered cytidine. The injected nucleoside produces a measureable increase of the concentrations of all three nucleotides. The increase produced by injecting 2.5 mol of cytidine for brain does not essentially change with higher doses of injected nucleoside, except for CMP, whose increase reaches a maximum with 5 mol of cytidine. A clear time dependence on cytidine administration was shown. The increases of the three nucleotide concentrations do not show a maximum till 60 min from administration of cytidine. The results indicate that administered cytidine is directly converted into CMP and CDP-bases and measurably increases their endogenous brain pools. The compound is likely to enter metabolic events connected with phospholipid metabolism in brain.     

Modification of lysine residues ofStaphylococcus aureus α-toxin: Effects on its channel-forming properties

Summary Staphylococcus aureaus -toxin opens an ion channel in planar phospholipid bilayers which is selective for anions over cations, supposedly because of the presence of positively charged groups along the ion pathway. To remove some positive charges of this protein toxin, we chemically modified part of its lysine residues either with diethylpyrocarbonate, followed by histidine regeneration with hydroxylamine, or with trinitrobenzenesulfonic acid. The extent of chemical modification can be followed accurately by native polyacrylamide gel electrophoresis and isoelectric focusing. Ethoxyformilation of two to three lysine residues per toxin monomer does not impair hemolysis of rabbit red blood cells nor formation of pores in model membranes. It reduces the conductance and the anion selectivity of the channel and changes the shape of its current-voltage characteristic. This indicates that positively charged lysine residues are actually important in determining the electrical properties of the pore. Ethoxyformilation of channels preassembled in planar bilayers produces the same changes as modification of toxin monomers before channel formation. Furthermore, it can be performed by adding diethylpyrocarbonate on either side of the bilayer. This suggests that the lysine residues relevant for the electrical properties of the pore are located inside its lumen where they can be reached by diethylpyrocarbonate diffusing from either entrance of the channel.     

An Exploration of the Effects of Constraints on the Phosphorylation of Synthetic Protein Tyrosine Kinase Peptide Substrates

We synthesized by classical solution methods three conformational constrained analogues of EDNEYTA, a heptapeptide sequence that represents the common major autophosphorylation site of the protein tyrosine kinases (PTKs) of the Src family. The correlation between the different structural properties induced by the modifications of the native sequence and the propensity of the peptides to act as PTK substrates was examined. The kinetic data obtained indicate that the introduction of the tyrosine-analogue constraints Tic(OH) and MeTyr, which block the ring flexibility, completely prevents the phosphorylation catalysed by the kinases Lyn and Fgr. On the other hand PTKIIB/p38^syk can phosphorylate the two derivatives albeit with an efficiency lower than that found with the native sequence. A third derivative contained side chain to side chain cyclization. This analogue, in which the freedom of the phenolic moiety is not altered, can be phosphorylated by all the PTKs tested with kinetic constants comparable to the parent peptide.     

Taxanes from Taxus x media

The roots of Taxus x media gave two new taxoids, the structures of which were established as 10-deacetyl-10-dehydro-7-acetyl taxol A and 10-deacetylyunnanxane on the basis of spectroscopic data.     

Apoptosis Dependent Decrease of the Intramembrane Ion Traffic in Cultured Mouse Fibroblasts Shown by Conductivity Dispersion

We have investigated the intramembranal ion traffic in apoptotic 3T6 cells in culture. Apoptosis was induced by various treatments, such as serum deprivation, high density growth and hydrogen peroxide at subnecrotic doses. Cell death was assessed by nucleosomal DNA fragmentation, single cell electrophoresis, immunofluorescence and histological staining. To study the modifications of membrane structure and function, we adopted a well established biophysical strategy based on the measurement of the electrical conductivity of cell suspensions, as a function of the frequency of the electrical field applied to the sample. A comparison between the conductivity of normal and apoptotic cell suspensions shows that programmed cell death causes a decrease of membrane conductivity which indicates a diminished intramembranal ion traffic. Our results strongly suggest that one of the early events in the triggering of apoptosis is represented by an overall reduction of plasma membrane function. Finally, our results are in agreement with the idea that the nucleus is not the sole target of the apoptotic process.     

Studies on cytochrome c. Part IV. Synthesis of the protected dodecapeptide (sequence 45–56) of Baker's yeast iso-1-cytochrome c

The synthesis is described for the N-benzyloxycarbonyldodecapeptide tert-butoxycarbonylhydrazide corresponding to the sequence 45–56 of baker's yeast iso-1-cytochrome c by fragment condensation using the Rudinger modified azide procedure for the assembly of the small subunits.     

Monazomycin channel noise

Spectral analyses of conductance fluctuations produced by monazomycin pores in black lipid membranes show slow (2 s), fast (30 ms) and ultra-fast (2 ms) kinetics. The extremely low level of this noise compared with the cationic permeability to large ions such Tris⁺ gives support to a model where only a small fraction of the total pore conductance is fluctuating.     

Systematics of the species of the yeast genus Saccharomyces associated with the fermentation industry

Summary The so-called wine yeasts Saccharomyces cerevisiae, S. chevalieri, S. bayanus, S. italicus and S. uvarum are characterized by high ethanol tolerance and fermentation velocity. They are ecologically related, being predominantly associated with grape must and wine, and are taxonomically indistinguishable. The only significant physiological differences are between the ability to ferment certain sugars. A taxonomic revision of more than 1,000 strains isolated during the past 50 years and belonging to the above species showed extreme instability in the ability to ferment different sugars. The relationships between these yeasts were examined for DNA base composition and DNA-DNA reassociation. The G+C ranged from 37.6% to 39.0% while optical reassociation experiments defined a first group of species (Saccharomyces cerevisiae, S. chevalieri and S. italicus) exhibiting high base sequence complementarity (>90%). S. bayanus and S. uvarum also showed a high degree of relatedness. Low homology values (30%) indicate that the two groups of species are not closely related. While it is proposed to combine S. cerevisiae, S. chevalieri and S. italicus into one single species under the oldest epithet Saccharomyces cerevisiae, a study of a larger number of strains is recommended before considering the taxonomic position of S. bayanus and S. uvarum.     

Serodiagnosis of acute hepatitis A

Hepatitis A antibody (anti-HAV) was detected by specific radioimmunoassay (RIA) method in sera from 10 patients with acute icteric hepatitis. Anti-HAV was detectable in many subjects very early before the onset of jaundice, but the diagnosis of type A hepatitis in all patients was confirmed by the demonstration of seroconversion during convalescence. Since the initial antibody detected by RIA is predominantly IgM, while IgG specific anti-HAV appears later reaching peak levels within 1 to 2 months, we treated serum specimens of these patients with 2-mercaptoethanol (2ME) in order to differentiate acute-from convalescent-phase hepatitis A sera. Inactivation of IgM fraction with 2ME produced a significant reduction of anti-HAV titer only in acute-phase sera, so that this procedure may be used for early diagnosis of acute type A hepatitis.