Unlike primary transport, secondary active transport utilizes energy stored in ions' electrochemical gradients, to transport solutes against their concentration gradients. One protein that exemplifies secondary active transport is the sodium-glucose-linked transporter or SGLT1. Initially, this transporter is positioned so that the cytosol facing side is closed, but the extracellular end is open. This exposes two negatively charged sodium-binding sites to the environment, which are then bound by positively charged sodium ions. Since more sodium ions populate the extracellular space than the cytoplasm, the transporter-bound sodium ions move down their electrochemical gradient. The sodium-bound transporter has a high affinity for glucose, present at a low-level outside but a high concentration inside the cell. A glucose molecule then attaches to the transporter against its concentration gradient, and this simultaneous binding of sodium and glucose causes the protein to close its extracellular region and open the cytoplasm facing side. The sodium ions then detach and enter the cytoplasm. This decreases the protein's affinity for glucose, releasing it into the cytoplasm. Once empty, the transporter returns to its initial orientation.