Antigen-antibody interaction at specific binding sites: A mechanism involving iminazole

Résumé L'auteur propose un mode de liaison entre les molécules d'antigène et d'anticorps au moyen d'un centre réactif spécifique résultant de l'interaction d'un groupe récepteur carboxylique de l'antig`ene avec le groupe iminazole d'une unite particuli`ere histidine de l'anticorps. Plusieurs faits viennent done confirmer l'hypoth`ese selon laquelle nous suggérons une analogie entre les interactions antig`eneanticorps et les interactions de certains enzymes et de leurs substrats.     

What causes mitochondrial DNA deletions in human cells?

Mitochondrial DNA (mtDNA) deletions are a primary cause of mitochondrial disease and are likely to have a central role in the aging of postmitotic tissues. Understanding the mechanism of the formation and subsequent clonal expansion of these mtDNA deletions is an essential first step in trying to prevent their occurrence. We review the previous literature and recent results from our own laboratories, and conclude that mtDNA deletions are most likely to occur during repair of damaged mtDNA rather than during replication. This conclusion has important implications for prevention of mtDNA disease and, potentially, for our understanding of the aging process.     

Variable effects of nitrogen additions on the stability and turnover of soil carbon

Soils contain the largest near-surface reservoir of terrestrial carbon and so knowledge of the factors controlling soil carbon storage and turnover is essential for understanding the changing global carbon cycle. The influence of climate on decomposition of soil carbon has been well documented, but there remains considerable uncertainty in the potential response of soil carbon dynamics to the rapid global increase in reactive nitrogen (coming largely from agricultural fertilizers and fossil fuel combustion). Here, using 14C, 13C and compound-specific analyses of soil carbon from long-term nitrogen fertilization plots, we show that nitrogen additions significantly accelerate decomposition of light soil carbon fractions (with decadal turnover times) while further stabilizing soil carbon compounds in heavier, mineral-associated fractions (with multidecadal to century lifetimes). Despite these changes in the dynamics of different soil pools, we observed no significant changes in bulk soil carbon, highlighting a limitation inherent to the still widely used single-pool approach to investigating soil carbon responses to changing environmental conditions. It remains to be seen if the effects observed here-caused by relatively high, short-term fertilizer additions-are similar to those arising from lower, long-term additions of nitrogen to natural ecosystems from atmospheric deposition, but our results suggest nonetheless that current models of terrestrial carbon cycling do not contain the mechanisms needed to capture the complex relationship between nitrogen availability and soil carbon storage.     

High levels of mitochondrial DNA deletions in substantia nigra neurons in aging and Parkinson disease

Here we show that in substantia nigra neurons from both aged controls and individuals with Parkinson disease, there is a high level of deleted mitochondrial DNA (mtDNA) (controls, 43.3% +/- 9.3%; individuals with Parkinson disease, 52.3% +/- 9.3%). These mtDNA mutations are somatic, with different clonally expanded deletions in individual cells, and high levels of these mutations are associated with respiratory chain deficiency. Our studies suggest that somatic mtDNA deletions are important in the selective neuronal loss observed in brain aging and in Parkinson disease.     

Treponemal infection in a Pleistocene bear

The age and origins of the organisms that cause syphilis (treponemes) have long been matters for controversy. The widely-held belief that Columbus's ship brought the disease from the New World to Europe rests on identification of the classic lesions in Inca, Aztec and Mississippian bones that date from 1,000 to 3,000 years before present. But these were not confirmed by immunological techniques. We have observed lesions characteristic of treponemal infection in a Pleistocene bear from Indiana (dated 11,500 years BP) which give a positive result when tested with the antisera used by the US Center for Disease Control for verification of syphilis infection. This is the earliest detection of treponemal disease using contemporary techniques.     

Excited complexes in photosensitized processes. Kinetic characteristics

Zusammenfassung Die Kinetik homogener Photoreaktionen, welche über einen Excimer-Komplex verlaufen, wird untersucht. Es ergibt sich, dass in Übereinstimmung mit zahlreichen Beobachtungen eine Konzentrationsabhängigkeit ähnlich der vonLangmuir-Hinshelwood für die heterogene Katalyse abgeleiteten zu erwarten ist.