Turnover of whole body proteins and myofibrillar proteins in middle-aged active men
Endurance-trained older men have a higher proportion of lean tissue and greater muscle cell oxidative capacity, reversing age-related trends and suggesting major changes in protein metabolism. In this study, protein turnover was determined in 6 middle-aged (52+/-1 yr) men who were well trained (VO/sub 2/ max 55.2+/-5.0 ml O/sub 2//kg.min) and lean (body fat 18.9+/-2.8%, muscle mass 36.6+/-0.6%). The maintained habitual exercise while consuming 0.6, 0.9 or 1.2 g protein/kg.day for 10-day periods. N flux was measured from /sup 15/N in urea after oral /sup 15/N-glycine administration. Myofibrillar protein breakdown was estimated from urinary 3-methyl-histidine. Dietary protein had no effect on turnover rates, even when N balance was negative. Whole body protein synthesis was 3.60+/-0.12 g/kg.day and breakdown was 3.40+/-0.14 g/kg.day for all N intakes. Whole body protein flux, synthesis and breakdown were similar to values reported for sedentary young (SY) or sedentary old (SO) men on comparable diets. 3-me-his (3.67+/-0.14 ..mu..mol/kg.day) was similar to values reported for SY but higher (p<0.01) than for SO. Myofibrillar protein breakdown per unit muscle mass (185+/-7 ..mu..mol 3-me-his/g creatinine) was higher (p<0.01) than for SY or SO. In active middle-aged men, myofibrillar proteins may account for a greater proportion of whole body protein turnover, despite an age-related reduction in muscle mass.
- Research Organization:
- Dept. of Agriculture, Boston, MA
- OSTI ID:
- 6858262
- Report Number(s):
- CONF-8604222-; TRN: 87-010466
- Journal Information:
- Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States), Vol. 45:4; Conference: 70. annual meeting of the Federation of American Society for Experimental Biology, St. Louis, MO, USA, 13 Apr 1986
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
PROTEINS
METABOLISM
EXERCISE
GLYCINE
HISTIDINE
MUSCLES
NITROGEN 15
TRACER TECHNIQUES
UREA
AMIDES
AMINO ACIDS
AZOLES
CARBONIC ACID DERIVATIVES
CARBOXYLIC ACIDS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
IMIDAZOLES
ISOTOPE APPLICATIONS
ISOTOPES
LIGHT NUCLEI
NITROGEN ISOTOPES
NUCLEI
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
STABLE ISOTOPES
550501* - Metabolism- Tracer Techniques