Final answer:
Membrane proteins are not very soluble in water because they have hydrophobic regions designed to interact with the lipid bilayer's non-polar core. Integral proteins embed within the membrane while peripheral proteins associate more loosely, both contributing to their poor water solubility. The structure and interaction with the lipid bilayer are essential for their function, such as facilitating molecule transport across the membrane.
Step-by-step explanation:
Why are Membrane Proteins Not Very Soluble in Water?
Membrane proteins are not very soluble in water due to their unique structure which allows them to interact with the non-polar regions of the cell's lipid bilayer. These proteins have hydrophobic (water-hating) regions that are designed to reside within the hydrophobic core of the lipid bilayer, where they can perform critical functions such as forming channels for ions, acting as signal transducers, and anchoring other molecules to the cell membrane. Integral membrane proteins span the hydrophobic interior of the bilayer and have regions that are compatible with the fatty acid environment of the membrane, helping them to maintain their proper structure and function within the lipid bilayer. On the other hand, peripheral proteins are associated more loosely with the lipid bilayer's surface through hydrogen bonding and electrostatic forces. The inherent hydrophobicity of integral and some peripheral proteins' domains make them difficult to be soluble in the aqueous, polar environment outside the membrane.
The difficulty in dissolving membrane proteins in water is amplified by the presence of hydrophobic alpha-helical domains that are essential for the proteins' interaction with the membrane's interior. These features make it challenging to isolate membrane proteins in a biologically active form, as in the case of comparing with cytochrome c, which can easily dissociate from the cristal membrane. Membrane transport proteins facilitate the passage of otherwise impermeable substances across the cell membrane, highlighting their importance in cellular function despite their low solubility in water.