1. Denoting a compound consisting of molecules that have only single bonds (i.e. no double or triple bonds). Saturated compounds can undergo substitution reactions but not addition reactions. See fatty acid. Compare unsaturated.
2. Describing a cellular transport system in which all the carrier molecules for a particular substance are fully loaded, so that the rate of transport across the plasma membrane is maximal.
3. Describing an enzyme molecule or system in which the active sites are fully occupied and the rate of reaction is determined primarily by how quickly the catalytic reaction takes place. It occurs when the substrate is present in excess, and as soon as each active site releases the product(s), another substrate molecule occupies it.
4. Describing a soil in which all the pores are filled with water.