Insulin receptor activation in hepatocytes. The receptor is denoted as R. One or two insulin molecules can bind to the receptor (green arrows). This is indicated by a prefix I or I 2, respectively. Receptor phosphorylation (blue arrows) is indicated by a suffix p, receptor internalization to the endosomal compartment (red arrows) is indicated by a subscript en. Arrows with two heads indicate reversible reactions. Arrows with one head indicate irreversible reactions. Filled arrowheads indicate positive direction of rates.