Mutagen-induced sister chromatid exchange rate in Bloom syndrome remains unaltered in the presence of Bloom corrective factor

Summary Fibroblasts of a patient with Bloom syndrome (GM-1492) were cultured in the presence of either mitomycin C, ethylmethanesulfonate, or 4-nitroquinoline-1-oxide, (4-NQ1-O) and sister chromatid exchange was determined. The mutagens enhanced the sister chromatid exchange rate to different degrees, 4-NQ1-O being the most potent substance. Bloom corrective factor, which is present in normal cell-conditioned culture medium, reduced the spontaneously increased SCE in Bloom syndrome cells by about 20 SCE per metaphase but failed to reduce the additional mutagen-induced SCE increase. These findings indicate that only spontaneously, but not mutagen-indeuced, SCE in Bloom syndrome fibroblasts can be decreased by the Bloom corrective factor.     

Nucleosomal distribution of thymine photodimers following far- and near-ultraviolet irradiation

The nucleosomal distribution of cis-syn cyclobutyl-type thymine photodimers was determined in normal human skin fibroblasts following irradiation with low doses of far-ultraviolet light at 254 nm and nearultraviolet light at 313 nm. The thymine photodimer concentrations were determined by high pressure liquid chromatography in acid hydrolysates of total cellular DNA and of nucleosomal core- and chromatosomal-DNA. The lesion concentrations in linker-DNA were calculated from these data. While thymine photodimers were distributed uniformely following 254 nm irradiation they were enriched by a factor of 2.4 – 4.2 in nucleosomal linker DNA after exposure to 313 nm light.     

Tetravalent Vanadium Releases Ferritin Iron which Stimulates Vanadium-Dependent Lipid Peroxidation

The iron storage protein, ferritin, represents a possible source of iron for oxidative reactions in biological systems. It has been shown that superoxide and several xenobiotic free radicals can release iron from ferritin by a reductive mechanism. Tetravalent vanadium (vanadyl) reacts with oxygen to generate superoxide and pentavalent vanadium (vanadate). This led to the hypothesis that vanadyl causes the release of iron from ferritin. Therefore, the ability of vanadyl and vanadate to release iron from ferritin was investigated. Iron release was measured by monitoring the generation of the Fe²⁺-fcrrozine complex. It was found that vanadyl but not vanadate was able to mobilize ferritin iron in a concentration dependent fashion. Initial rates. and iron release over 30 minutes. were unaffected by the addition of superoxide dismutase. Glutathione or vanadate added in relative excess to the concentration of vanadyl, inhibited iron release up to 45%. Addition of ferritin at the concentration used for measuring iron release prevented vanddyl-induced NADH oxidation. Vanadyl promoted lipid peroxidation in phospholipid liposomes. Addition of ferritin to the system stimulated lipid peroxidation up to 50% above that with vanadyl alone. Fcrritin alone did not promote significant levels of lipid peroxidation.     

Ferritin, Lipid Peroxidation and Redox-Cycling Xenobiotics

A number of xenobiotics are toxic because they rcdox cycle and generate free radicals. Interaction with iron, either to produce reactive species such as the hydroxyl radical, or to promote lipid peroxidation, is an important factor in this toxicity. A potential biological source of iron is ferritin. The cytotoxic pyrimidines, dialuric acid, divicine and isouramil, readily release iron from ferritin and promote ferritin-dependent lipid peroxidation. Superoxide dismutase and GSH, which maintain the pyrimidines in their reduced form, enhance both iron release and lipid peroxidation. Microsomes plus NADPH can reduce a number of iron complexes, although not ferritin. Reduction of Adriamycin. paraquat or various quinones to their radicals by the microsomes enhances reduction of the iron complexes, and in some cases, enables iron release from ferritin. Adriamycin stimulates iron-dependent lipid peroxidation of the microsomes. Ferritin can provide the iron, and peroxidation is most pronounced at low PO₂. Compiexing agents that supress intraccllular iron reduction and lipid peroxidation may protect against the toxicity of Adriamycin.     

The baboon model under anesthesia for in vivo cerebral blood flow studies using single photon emission computed tomographic (SPECT) techniques.

Single photon emission computed tomography of the brain can be useful in animal experimentation directed toward cerebral conditions. A well established and understood baboon model, necessarily under anesthesia, could be especially valuable in such investigations. Six normal baboons were studied under various anesthetic agents and their combinations: ketamine, thiopentone, pentobarbitone, and halothane. Cerebral blood flow (CBF) studies were performed with 99mTc-HMPAO. CBF effects from various anesthesia were detected, requiring careful choice of the anesthesia for cerebral investigations.     

Dynamic nature of the quaternary structure of the vesicular stomatitis virus envelope glycoprotein

The envelope glycoprotein (G protein) of vesicular stomatitis virus probably exists in the viral envelope as a trimer of identical subunits. Depending on the conditions of solubilization, G protein may dissociate into monomers. G protein solubilized with the detergent octyl glucoside was shown to exist as oligomeric forms by sedimentation velocity analysis and chemical cross-linking. G protein was modified with either fluorescein isothiocyanate or rhodamine isothiocyanate. Resonance energy transfer between fluorescein and rhodamine labels was observed upon mixing the two labeled G proteins in octyl glucoside. This result provided further evidence that G protein in octyl glucoside is oligomeric and indicated that the subunits are capable of exchange to form mixed oligomers. Resonance energy transfer was independent of G protein concentration in the range examined (10-80 nM) and was not observed when labeled G proteins were mixed with fluorescein or rhodamine that was not conjugated to protein. Resonance energy transfer decreased upon incorporation of G protein into Triton X-100, consistent with sedimentation velocity data that G protein in Triton X-100 is primarily monomeric. Kinetic analysis showed that the subunit exchange reaction had a half-time of about 3 min at 27 degrees C that was independent of G protein concentration. These data indicate that the exchange occurs through dissociation of G protein trimers into monomers and dimers followed by reassociation into timers. Thus, in octyl glucoside, G protein must exist as an equilibrium between monomers and oligomers. This implies that monomers are capable of self-assembly into trimers.     

Functions and relevance of the terminal complement sequence

The terminal complement sequence is initiated upon cleavage of C5 with liberation of C5a anaphylatoxin, and involves the assembly of macromolecular C5b-9 complexes either on cell surfaces or in plasma. Cell-bound C5b-9 complexes generate transmembrane pores that can cause cell death, or they can elicit secondary cellular reactions triggered, for example, by passive flux of calcium ions into the cells. In vivo functions of the fluid-phase SC5b-9 complex have not yet been defined, but the identity of S-protein with vitronectin (serum spreading factor) provokes the anticipation that significant biological functions of this complex do exist. The terminal complement sequence may fulfil protective functions when it is triggered on alien cells that are marked for destruction. Dysregulation in the complement sequence may, however, result in detrimental attack by C5b-9 on autologous cells. Examples include not only autoimmune disease states, but also the activation of complement on dead or dying cells, and bystander attack on blood cells during cardiopulmonary bypass. Methods for detecting and quantifying C5b-9 are outlined, and the potential usefulness of such assays in clinical research is discussed.     

GC subtyping and HIV infection in a Spanish population: no evidence of an association between GC subtypes and AIDS

Group-specific component (GC) subtyping was performed by isoelectric focusing in 318 Spanish drug users at risk for infection or infected by HIV (85 HIV seronegatives, 111 HIV seropositives without symptoms, 89 seropositives with symptoms, 33 AIDS patients) and 187 healthy individuals. There was no significant association between GC subtypes and susceptibility to HIV infection and/or progression to AIDS.