Insulin stimulates the phosphorylation of ribosomal protein S6 in a cell-free system derived from 3T3-L1 adipocytes

Physiological concentrations of insulin stimulate the incorporation of ³²P into ribosomal protein S6 in intact 3T3-L1 adipocytes. Extracts from cells treated with insulin also exhibit an increased ability to incorporate ³²P from [γ-³²P]ATP into protein S6 in vitro. The authors now report that the direct addition of insulin to particulate preparations containing high affinity insulin receptors and ribosomes derived from insulin-sensitive cells (not previously exposed to insulin) stimulates incorporation of ³²P from [γ-³²P]ATP into ribosomal protein S6 1.5- to 3.0-fold. The stimulation occurs at the same concentrations of insulin (0.1-1.0 nM) and within the same period of time as it does in intact cells.