"Under physiological conditions, virtually all vitamin A in the blood is not in its free form but bound to its high-affinity carrier protein. If this carrier protein is like a boat that carries vitamin A, how does it know when to unload its cargo? It was proposed more than 30 years ago that a cell-surface receptor exists that specifically binds to the carrier protein and mediates vitamin A uptake."
METAMIA is a free database of analogy and metaphor. Anyone can contribute or search. The subject matter can be anything. Science is popular, but poetry is encouraged. The goal is to integrate our fluid muses with the stark literalism of a relational database. Metamia is like a girdle for your muses, a cognitive girdle.