Radiation-induced reductive modifications of sulfur-containing amino acids within peptides and proteins.

The complex scenario of radical stress reactions affecting peptides/proteins can be better elucidated through the design of biomimetic studies simulating the consequences of the different free radicals attacking amino acids. In this context, ionizing radiations allowed to examine the specific damages caused by H-atoms and electrons coupled with protons, thus establishing the molecular basis of reductive radical stress. This is an innovative concept that complements the well-known oxidative stress also in view of a complete understanding of the global consequences of radical species reactivities on living systems. This review summarizes the knowledge of the chemical changes present in sulfur-containing amino acids occurring in polypeptides under reductive radical conditions, in particular the transformation of Met and Cys residues into α-amino butyric acid and alanine, respectively. Reductive radical stress causing a desulfurization process, is therefore coupled with the formation of S-centered radicals, which in turn can diffuse apart and become responsible of the damage transfer from proteins to lipids. These reductive modifications assayed in different peptide/protein sequences constitute an integration of the molecular inventories that up to now take into account only oxidative transformations. They can be useful to achieve an integrated vision of the free radical reactivities in a multifunctional system and, overall, for wider applications in the redox proteomics field.

[Effect of local x-ray irradiation of the abdominal area on the amino acid content of the blood plasma and their urinary excretion in dogs and rats]. / Vliianie lokal'nogo rentgenovskogo oblucheniia oblasti zhivota na soderzhanie aminokislot v plazme krovi i ékskretsiiu ikh s mochoi u sobak i krys.

A study was made of the content of amino acids in blood plasma of dogs and rats and daily excretion thereof from rat body in urine after local X-irradiation of abdomen with a dose of 13.5 Gy. As the gastrointestinal syndrome developed the content and excretion of taurine increased, glucogenic amino acid content of plasma decreased, and the ratio of phenylalanine to tyrosine and branched-chain amino acids to aromatic amino acids changed. The ratio of arginine to ornithine and urea to ammonia sharply dropped in animals, which died later on, indicating that the urea-producing function of liver was impaired and hyperammonemia developed.