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Age-Related Decline in Actomyosin Function

¹ Department of Biochemistry, Molecular Biology, and Biophysics
² Department of Physical Medicine and Rehabilitation, University of Minnesota, Minneapolis.

Address correspondence to Ewa Prochniewicz, Department of Biochemistry, University of Minnesota, Jackson Hall 6-155, 321 Church Street, Minneapolis, MN 55455. E-mail: ewa{at}ddt.biochem.umn.edu

To understand the molecular basis of the functional decline in aging muscle, we examined the functional (actomyosin ATPase) and chemical (cysteine content) changes in actin and myosin purified from the muscles of young (4- to 12-month-old) and old (27- to 35-month-old) Fisher 344 rats. Using the soluble, catalytically active myosin fragment, heavy meromyosin (HMM), we determined the maximum rate (V_max) and actin concentration at half V_max (K_m) of the actomyosin ATPase, using four combinations of actin and HMM from old and young rats. V_max and K_m were significantly lower when both actin and HMM were obtained from old rats than when both proteins were obtained from young rats. The number of reactive cysteines in HMM significantly decreased with age, but no change was detected in the number of reactive cysteines in actin. We conclude that aging results in chemical changes in myosin (probably oxidation of cysteines) that have inhibitory effects on the actin-activated myosin ATPase.