Radical formation in the reactions of hydrogen atoms with some cystinefree proteins and polyalanine was investigated by both ESR and tritiumlabeling techniques. The results show that hydrogen atoms can cause chain cleavage as well as lead to the formation of carbon radicals. In the case of histone a large proportion (67%) of the carbon radicals is on lysine residues. The distribution of radicals observed for hydrogen atom bombardment was similar to that observed in gamma radiolysis for samples of histone, nagarse, and poly-DL-alanine. Reasons for this similarity are discussed. Exposure to hydrogen atoms produces α-carbon radicals in poly-DL-alanine and chain cleavage in poly-L-alanine, demonstrating that conformation affects the secondary radical distribution.

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