Effects of physical training on skeletal muscle metabolism and ultrastructure in 70 to 75-year-old men

The effects of a 12-week program of physical training on skeletal muscle (vastus lateralis) characteristics in 5 old men were investigated. Heart rates during submaximal bicycle exercise were decreased after training, indicating an improved cardiovascular function. As judged from enzyme activity measurements, the anaerobic capacity as well as the mitochondrial oxidative capacity were increased by the training. Fatty acid oxidation capacity remained unchanged, while the glycolytic potential tended to be increased, suggesting a somewhat different pattern of adaptation as compared to that seen in young subjects. Volume fractions of mitochondria and lipid droplets were unchanged with training, supporting the view that in old men, increases in oxidative capacity take place within the existing mitochondrial volume. It was concluded, that the aging human skeletal muscle remains trainable, and that the training response is similar, but possibly not identical, to that seen in younger age groups.     

Design of protecting groups for the β-carboxylic group of aspartic acid that minimize base-catalyzed aspartimide formation

With the objectives of developing new protecting groups for the β-carboxyl group of aspartic acid that are resistant to base-catalyzed aspartimide formation and of evaluating the importance of sterical factors in the design of such protecting groups, four new alkyl ester derivatives of aspartic acid were synthesized. The β-3-pentyl, β-4-heptyl, β-2,6-dimethyl-4-heptyl and the recently described β-2,4-dimethyl-3-pentyl esters of Boc-aspartic acid were incorporated into model peptides, and the resin-bound protected peptides were treated with 20% pipetidine for 10 h. The levels of aspartimide-related side products were compared with the previously reported β-cyclohexyl, β-menthyl and β-2-adamantyl esters of aspartic acid. The results show that bulky, acyclic, aliphatic protecting groups (in particular the 2,4-dimethyl-3-pentyl ester) are significantly more resistant to base-catalyzed aspartimide formation than comparably rigid cyclic alkyl esters that under the same reaction conditions form several-fold more aspartimide-related side products. Using elevated temperatures to overcome difficult couplings leads to the formation of significant amounts of aspartimide when aspartic acid is protected with the cyclohexyl group, but the 2,4-dimethyl-3-pentyl protecting group offers excellent protection under these conditions. The use of the 2,4-dimethyl-3-pentyl protecting group will allow the use of orthogonally removable base-labile protecting groups in Boc chemistry and suggests a design of protecting groups for other nucleophile-sensitive trifunctional amino acids in both Boc and Fmoc chemistry. © Munksgaard 1996.