MadSci Network: Cell Biology

Re: Difference between hemoglobin and myoglobin?

Date: Mon Sep 22 15:22:01 2003
Posted By: Michael Maguire, Professor
Area of science: Cell Biology
ID: 1064248287.Cb

I'm not sure where you get the idea that one protein is hydrophilic and 
one hydrophobic.  Both are quite soluble proteins and therefore 
predominately, in relative terms, hydrophilic.  Both certainly have a 
number of what would normally be considered hydrophobic amino acids.  
Hemoglobin has a slightly higher percentage of these, but this is because 
it is an a2b2 tetramer whereas myoglobin is a monomer.  Thus the entire 
surface of myoglobin is in contact with water and must therefore be, again 
in relative terms, hydrophilic.  In contrast, the tetrameric structure of 
hemoglobin means that a significant amount of protein surface area is in 
contact not with water but with some other part of the tetrameric 
protein.  Protein-protein contacts can be formed either from 
hydrophobic/hydrophobic interactions or hydrophilic/hydrophilic, rarely 
from a mixture.  Most such protein-protein interactions are relatively 
hydrophobic.  Simple consideration of the geometry will show that a higher 
percentage of surface amino acids on hemoglobin will be hydrophobic 
compared to myoglobin even though their overall structures are quite 

If this doesn't answer your question or doesn't make sense, I'll try again.

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