A series of lactam-bridged and linear 14 residue amphipathic alpha-helical peptides based on the sequence Ac-EXEALKKEXEALKK-amide were prepared in order to determine the effect of decreasing the hydrophobicity of the nonpolar face to helical content and stability. This was done by substituting position X by Ile, Val, and Ala. Lactam bridges spaced i to i + 4 were formed between the side chains of Glu3 and Lys7 and Glu10 and Lys14 while the linear noncyclized peptides could potentially form i to i + 4 salt bridges with the same residues. It was found that in all cases the lactam-bridged peptides were substantially more helical than the corresponding linear peptides as determined by CD spectroscopy. Moreover, the helical content approached 100% for the lactam-bridged peptides X = Ile and Ala and was greater than 80% for X = Val. For X = Ile and Val, this was partly due to the ability of the lactam bridges to enhance interchain interactions relative to the linear versions of the same sequence. Size-exclusion chromatography demonstrated that the Ile-based peptide associates as a dimer. The alanine-based lactam-bridged peptide was found to be monomeric as determined by concentration dependency studies and size-exclusion chromatography. Thermal denaturation studies in benign media indicated that the lactam-based peptides were very stable. The conformation of the Ala-based lactam peptide was further characterized by two-dimensional NMR spectroscopy and was found to be highly helical. The results demonstrate the ability of lactam bridges to stabilize the helical conformation and enhance dimerization of peptides based on a 3,4 hydrophobic heptad repeat. The substitution of Ala residues in the hydrophobic face of the alpha-helix can prevent dimerization and specify monomeric helical structure.

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Physiologic and skeletal muscle characteristics of a world champion and world record holder Masters distance runner were evaluated in the context of his race performances at age 50 and 51. Comparisons were made to data on other middle-aged runners and on younger, elite distance runners. The subject had a VO2 max of 62.6 mL.kg-1.min-1, an average value for elite, middle-aged runners, but a low value compared to elite, younger distance runners. The subject had a smaller proportion of ST fibers in his gastrocnemius muscle (51.9%) compared to elite distance runners (mean 70.7%) However, the subject had a higher phosphorylase activity and a succinate dehydrogenase activity that was in the same range for younger, elite distance runners. In addition, the subject's gastrocnemius muscle was characterized by small ST and FT fibers with a large capillary density, favoring oxygen diffusion. Despite a relatively modest VO2 max value, the subject has demonstrated superior performance criteria in races from 3 to 42.2 km and an apparent ability to run for several hours at a high percentage of his VO2 max. These capabilities correspond to his large muscle metabolic capacity and enhanced muscle capillarization.