Thus, in order to delve in detail into the nutrient-sensing pathways and how they go awry in metabolic disorders, the researchers focused on an enzyme called p70 S6 Kinase 1, or S6K, which plays a role in regulating the growth and proliferation of all cells, including nerve cells.
It turns out that this enzyme, and the pathway it regulates, is nutrient sensitive - that is, S6K activity increases in the presence of carbohydrates and protein.
To test their hypothesis, the researchers injected rats with special viruses that selectively raise or lower S6K activity.
When we lowered S6K activity, we saw essentially the opposite response," said Dr.
Schwartz said that it was important how increased S6K activity reduced the rats' food intake by reducing the average size of meals rather than changing the number of meals over the course of a day.
In another experiment, the researchers tested whether increased S6K activity would protect against the natural tendency of mammals on a high-fat diet to overeat.
On the whole, the study shows that S6K acts as a kind of food-sensing thermostat in mammals, increasing or decreasing feeding behaviour and metabolism to maintain a normal energy balance.
The fragment of residues (231 to 236) is the recognition sequence of S6K (Figure 2B).
Previously, the function of S6K was also thought to correlate with this effect (Flotow and Thomas, 1992).
Ribosomal protein S6 is well-characterized downstream molecule that is regulated by S6K and S6K is the only proven S6 S240/244 phosphorylating enzyme in mammalian cells.
Ribosomal protein S6 (rpS6) is a well-characterized downstream molecule that is regulated by p70S6K
, and for at least 10 yrs after the discovery of S6K
, rpS6 was believed to be its only substrate.