A complex of two proteins, which in animals is 50kDa and consists of the insulin-like growth factor (IGF) and one of the insulin-like growth factor binding protein-1 (IGFBP-1), -2 (IGFBP-2), -4 (IGFBP-4) and -6 (IGFBP-6). The complex plays a role in growth and development.
IGF binary complex