Amino acid contacts between histones are the same for plants and mammals. Binding-site studies using ultraviolet light and tetranitromethane.

Leek chromatin has been cross-linked by UV light and tetranitromethane. The same major H2A--H2B and H2B--H4 cross-linked dimers are formed as in mammalian chromatin. CNBr peptide mapping shows that the cross-links occur in the same regions of the histone sequence for both plants and mammals. Interspecies complexes formed between leek and calf H2A and H2B can be cross-linked by UV light with the same specificity as intraspecies H2A--H2B complexes. We conclude that certain geometric features of histone-histone binding sites are conserved precisely during evolution despite large changes in the overall histone sequence. Moreover, our data show that identification of cross-linked amino acids using binding-site probes such as UV light and tetranitromethane can yield significant information about thermodynamically important contacts within histone-histone binding sites.

On the mechanism of nucleosome unfolding.

We have studied the relative stabilities to urea denaturation of histone-histone binding interactions as they occur both in chromatin and in histone complexes free in solution. We have used the two zero-length contact-site cross-linking agents, tetranitromethane and UV light, to measure the relative degree of H2B-H4 and H2A-H2B association under various conditions. The two interactions were disrupted coordinately when nuclei were treated with increasing concentrations of urea. In contrast, when histone complex in 2 M NaCl were treated with urea, the H2B-H4 interaction was found to be much less stable than the H2A-H2B interaction. We have shown previously that nucleosomes unfold at low ionic strengths such that the H2B-H4 but not the H2A-H2B interaction is broken in the process. We speculate that the preferential rupture of the H2B-H4 contact is of physiological significance.

Treatment of theophylline toxicity with oral activated charcoal.

Oral activated charcoal was administered to 4 patients with theophylline toxicity, who had gastrointestinal and neurologic symptoms as well as cardiac arrhythmias. Administration of oral charcoal significantly reduced the theophylline half-life in the serum of each patient. The charcoal was well tolerated and symptoms of toxicity rapidly resolved. We conclude that administration of oral charcoal rapidly reduces the serum theophylline concentration and should be used as the initial treatment in patients with theophylline toxicity.

Specific histone-histone contacts are ruptured when nucleosomes unfold at low ionic strength.

The ordered unfolding of the nucleosome core within chromatin at low ionic strengths has been studied. The results show that, when nuclei are lysed gently in solutions of very low ionic strength, their constituent nucleosomes rupture at a major H2B-H4 binding site but remain unperturbed at the site of the H2A-H2B interaction. These conclusions are based on data which show that at least four separate but closely spaced H2B-H4 contacts, identifiable by contact-site cross-linking in intact nuclei, are broken when nuclei are suspended in very dilute buffers. Appropriate controls on purified nucleosomes monomers demonstrate that the H2B-H4 contacts being broken are indeed intranucleosomal. Sedimentation of nucleosomes in the ultracentrifuge at various salt concentrations reveals that a significant conformational transition occurs in the range of ionic strength over which the H2B-H4 binding site ruptures.

Increased serum theophylline clearance with orally administered activated charcoal.

The purpose of this study was to determine whether the oral administration of activated charcoal would increase the clearance of theophylline. Seven normal subjects received aminophylline intravenously (8 mg/kg) on 2 separate days. On Day 1 at 2-h intervals starting immediately after the completion of the aminophylline infusion, subjects ingested 4 doses of a slurry of activated charcoal (30 g each). On Day 2 they received no charcoal. The order of the days the subjects received charcoal or no charcoal was randomized. Plasma theophylline levels were determined by an enzyme immunoassay (Syva) every 2 h after the completion of the intravenous infusion. The theophylline half-life was reduced with charcoal from 10.2 to 4.6 h (p less than 0.001), and clearance increased from 35.6 to 72.6 ml/kg/h (p less than 0.001). In a patient with an initial serum theophylline concentration of 31.0 micrograms/ml and signs of toxicity (arrhythmias and seizures), the administration of charcoal (4 doses of 30 g every 2 h) reduced the half-life from 34.4 to 5.7 h concomitant with rapid resolution of signs of toxicity. We conclude that orally administered activated charcoal significantly enhances the clearance of theophylline and offers a new therapeutic modality in the treatment of theophylline toxicity.