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Peroxynitrite is an extremely reactive entity and has in vivo existence. Its interaction with biomolecules may cause oxidation and nitration. In this study, commercially available H2A histone was exposed to peroxynitrite generated in vitro. The peroxynitrite‐mediated structural changes in histone were studied by ultraviolet & fluorescence spectroscopy, high performance liquid chromatography, anilinonaphthalene‐8‐sulfonic acid binding and polyacrylamide gel electrophoresis. Analysis of results revealed that carbonyl, nitrotyrosine and dityrosine contents were significantly increased in peroxynitrite‐modified H2A compared with native H2A. Rabbits challenged with peroxynitrite‐modified H2A induced high titre antibodies. The immunogenicity of peroxynitrite‐modified H2A was directly proportional to protein nitrotyrosine content and induced antibodies showed specificity for the immunogen and good cross‐reaction with nitrated epitopes of other modified proteins. Formation of high molecular weight immune complex with retarded mobility further supports the specificity of induced anti‐100 μm peroxynitrite‐modified H2A antibodies for the immunogen. It may be concluded that induction of anti‐H2A histone antibodies could be due to protection of peroxynitrite‐modified histone from proteolytic breakdown and its subsequent recognition by immunoregulatory cells as foreign molecule.

The spectrum of Br IV has been studied in the wavelength region 320–1290 Å based on the recordings made on a 3-m normal incidence spectrograph at Antigonish Laboratory and on a 6.65-m grazing incidence spectrograph at Zeeman Laboratory, Amsterdam.The light sources used were a triggered spark and sliding spark, respectively. The 4s24p2–[4s4p3+4s24p (4d+5d+6d+5s+6s+7s)] transition array has been investigated using Hartree–Fock (HF) and least squares fitting (LSF) parametric calculations. Previous analysis has been revised and extended considerably. A value of 1S0 level of the ground configuration 4s24p2 has been found at 33575.5 cm−1. One hundred and forty-two lines have been classified in this spectrum to establish 61 energy levels out of which 43 are new. The wavelength accuracy of our measurements for sharp lines is ±0.005 Å. A revised value of the ionization potential of Br IV has been found to be 385 400±250 cm−1 (47.77±0.03 eV).

The spectrum of cesium was recorded in the 300–1250 Å on a 3 m normal incidence spectrograph using a triggered spark source. The 5s25p3 (6d + 7s) configurations in Cs IV spectrum were investigated. 41 out of 47 levels of two configurations have been established on the basis of 76 lines in the 344 Å–949 Å region. The observed spectrum was interpreted satisfactorily by carrying out Hartree–Fock (HF) and least-squares-fitting (LSF) calculations using Cowan Code.

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