Which protein classes are not typically found in the membrane?

Hormones are a class of proteins that primarily function in signaling and regulation within the body, often operating through the bloodstream rather than being embedded in cellular membranes. While some hormone receptors may be located in the membrane to receive signals from their respective hormones, the hormones themselves usually circulate throughout the body and bind to these receptors, initiating specific biological responses.

In contrast, enzymes, receptors, and transport proteins are typically associated with cellular membranes. Enzymes may be integrated into the membrane or function on the membrane's surface to catalyze reactions. Receptors are crucial components of signaling pathways, allowing cells to respond to external signals, and are often integral or peripheral membrane proteins. Transport proteins, including channels and carriers, play essential roles in facilitating the movement of molecules across the membrane, which is vital for maintaining cellular homeostasis and communication. Thus, hormones do not typically reside in the membrane, making this choice appropriate in the context of the question.