PI3K

Phosphatidylinositol 3-kinase (PI3K)
PI3K adds a phosphate group to the 3C position in a inosital ring in Phosphatidylinositol.
example: PI-4,5-phosphate (PIP2) + ATP ----> PI-3,4, 5-bisphosphate (PIP3) + ADP
This in the context of the Insulin pathway allows the resulting PIP3 to remain bound to the plasma membrane.This initiates a signal cascade which can cause GLUT 4 translocation, decreased synthesis of glycerol and fatty acids, increased glycogen synthesis and increased protein synthesis in the cell.
Structure: Has 2 subunits:
1. Regulatory subunit, p85 (85 KDa), contains 2 SH2 domains and 1 SH3 domain.
2. Catalytic subunit, p110 (110KDa).
The SH2 domain in the context of the Insulin pathway binds p85 to phosphorylated tyrosines on the Insulin receptor substrate (IRS). The SH3 domain targets the proline rich section of p85 binding both regulatory and catalytic subunits together.