[Nonenzymatic deamidation as a factor in protein aging]

Amidation of two protein fractions of brain, heart and liver of senite rats was found to decrease by 15--21% as compared with that of young animals. This decrease was shown to be due to unstable amide groups. Strong evidence is presented favouring the preposition that in proteins the unstable amide groups are those of asparagine and the stable ones those of glutamine. The possibility of the nonenzymatic deamidation of proteins was investigated. Deaminated proteins were found to be more easily attacked by proteinases which could be one of the possible ways of breakdown of aging proteins.