In the plasma membrane, the best method to study the properties of integral membrane proteins is

The correct option is freeze fracture analysis and electron microscopy.

In the study of cell biology, understanding the structure and distribution of integral membrane proteins within the lipid bilayer poses a unique challenge. Because the plasma membrane consists of a fluid phospholipid bilayer with embedded proteins, standard imaging techniques often fail to reveal the internal organization of these membranes.

Freeze fracture is a specialized technique designed to overcome this challenge:
1. Freezing: The biological specimen is rapidly frozen in liquid nitrogen to preserve its structure in a lifelike state.
2. Fracturing: The frozen specimen is struck with a cold knife under a vacuum. Due to the hydrophobic nature of the interior of the lipid bilayer, the fracture plane preferentially travels through the hydrophobic core, splitting the lipid bilayer into two halves: the extracellular face (E-face) and the protoplasmic face (P-face).
3. Replication: A thin layer of metal (such as platinum) followed by carbon is evaporated onto the fractured surface to create a replica of the topography.
4. Observation: The organic material is dissolved away, and the replica is examined using transmission electron microscopy (TEM).

When examined under the electron microscope, the integral membrane proteins, which span across the lipid bilayer, remain associated with one of the half-membranes and appear as distinct bumps or "intramembranous particles" (IMPs) against a smooth background of lipid. This allows researchers to directly visualize, map, and study the distribution, size, and properties of integral membrane proteins in their native membrane environment.