All mammalian cells contain trans-membrane transport systems for the stereo specific uptake of glucose. These systems are divided into two groups, a facilitated diffusion system driven by the concentration differences across the membrane and an energy-dependent, active transport system. Both are mediated by specific membrane proteins, termed glucose transporter. The facilitated glucose transporters comprise a structurally related family of proteins having 12 membrane-spanning domains, with the amino terminus, a relatively large middle loop and the carboxy-terminus all oriented towards the cytoplasm. The active glucose transport system is also designated Na+/glucose cotransporter, SGLT, the predicted secondary structure of which is still controversial.