Absolute Quantitative Profiling of the Key Metabolic Pathways in Slow and Fast Skeletal Muscle

Slow
and fast skeletal muscles are composed of, respectively, mainly
oxidative and glycolytic muscle fibers, which are the basic cellular
motor units of the motility apparatus. They largely differ in excitability,
contraction mechanism, and metabolism. Because of their pivotal role
in body motion and homeostasis, the skeletal muscles have been extensively
studied using biochemical and molecular biology approaches. Here we
describe a simple analytical and computational approach to estimate
titers of enzymes of basic metabolic pathways and proteins of the
contractile machinery in the skeletal muscles. Proteomic analysis
of mouse slow and fast muscles allowed estimation of the titers of
enzymes involved in the carbohydrate, lipid, and energy metabolism.
Notably, we observed that differences observed between the two muscle
types occur simultaneously for all proteins involved in a specific
process such as glycolysis, free fatty acid catabolism, Krebs cycle,
or oxidative phosphorylation. These differences are in a good agreement
with the well-established biochemical picture of the muscle types.
We show a correlation between maximal activity and the enzyme titer,
suggesting that change in enzyme concentration is a good proxy for
its catalytic potential in vivo. As a consequence,
proteomic profiling of enzyme titers can be used to monitor metabolic
changes in cells. Additionally, quantitative data of structural proteins
allowed studying muscle type specific cell architecture and its remodeling.
The presented proteomic approach can be applied to study metabolism
in any other tissue or cell line.