Protein nitration with aging in the rat semimembranosus and soleus muscles.

On the basis of the accelerated age-related effects in type II muscle, we hypothesized that with aging the semimembranosus (type II) muscle would accumulate a greater amount of oxidized proteins compared to proteins in the soleus (type I) muscle. In this study, 3-nitrotyrosine (3-NT) was used as a stable marker of protein oxidative damage. The presence of 3-NT was evaluated in muscles from young adult, old, and very old Fischer 344 rats to provide an indication of the time course of muscle protein oxidative damage. A significant age-associated increase in nitrotyrosine-modified proteins was observed. The modified proteins identified by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry include the sarcoplasmic reticulum Ca(+2)-ATPase, aconitase, beta-enolase, triosephosphate isomerase, and carbonic anhydrase III. These proteins, involved in metabolism and calcium homeostasis, exhibited an age-dependent increase in 3-NT content in both muscles. However, significant levels of 3-NT modification were present at an earlier age in the semimembranosus muscle.