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1 Noll Physiological Research Center, Pennsylvania State University, University Park, PA, USA
2 Department of Chemistry, Pennsylvania State University, University Park, PA, USA
3 Noll Physiological Research Center, Pennsylvania State University, University Park, PA, USA; Department of Cellular and Molecular Physiology, Pennsylvania State University, Hershey, PA, USA; Clinical Neurophysiology, Uppsala University, Uppsala, Sweden
* To whom correspondence should be addressed. E-mail: Lars.Larsson{at}neurofys.uu.se.
Non-enzymatic glycosylation (glycation) has been recognized as an important post-translational modification underlying alterations of structure and function of extracellular proteins during aging and diabetes. Intracellular proteins may also be affected by this modification and glycation has been suggested to contribute to the aging-related impairment in skeletal muscle function. Glycation is the chemical reaction of reducing sugars with primary amino groups resulting in the formation of irreversible Advanced Glycation End-products (AGEs). Glutathione, primarily an antioxidant, is an abundant tripeptide in skeletal muscle. In order to understand the effect of glutathione on glycated myosin function, we used a single fiber in vitro motility assay, i.e., where myosin is extracted from a single muscle fiber segment to propel fluorescent-labeled actin filaments. Myosin function responded to glucose exposure in a dose-dependent manner, i.e., motility speeds were reduced by 10, 34, and 90% of pre-incubation values after 30 minutes exposure to 1, 3 and 6 mM glucose concentration, respectively. The 30-minute 6 mM glucose incubation was followed by a 20-minute 10 mM glutathione incubation. Glutathione treatment restored motility (0.98 ± 0.06 µm/s, n=3) (p<0.001) after glucose exposure (0.10 ± 0.07 µm/s, n=3), close to pre-incubation levels (1.12 ± 0.06 µm/s, n=3). It is concluded that glucose modifies myosin function in a dose-dependent manner and that glutathione reverses the effect of glucose on myosin function.
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