The cotransport of proteins that allows two different substances to pass through a membrane in the same direction is called symport.

Here's a breakdown:

* Cotransport: This refers to the movement of two or more substances across a membrane at the same time.

* Symport: A specific type of cotransport where both substances move in the same direction across the membrane.

Example:

A classic example is the sodium-glucose symporter found in the small intestine. This protein simultaneously transports both sodium ions (Na+) and glucose molecules into the intestinal cell. The movement of Na+ down its concentration gradient provides the energy for the movement of glucose against its concentration gradient.

Let me know if you'd like more details about symport or other types of membrane transport!