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To describe the two types of active transporter proteins, we must first understand that active transport is a process in which substances are moved across cell membranes against their concentration gradient, requiring energy in the form of ATP. Transporter proteins facilitate this process. There are two main types of active transporters: primary and secondary. 1. Primary active transporters directly use ATP to pump substances across the cell membrane. An example of a primary active transporter is the Sodium-Potassium pump (Na+/K+-ATPase) that maintains the electrochemical gradient in animal cells. 2. Secondary active transporters rely on the electrochemical gradient created by primary active transporters. They use the energy from the movement of one substance to facilitate the movement of another substance and can be classified into symport and antiport systems. An example of secondary active transport is the Sodium-Glucose Transporter-1 (SGLT1) in the intestine, which uses the sodium gradient created by the Sodium-Potassium pump to transport glucose from the intestine into cells.