The Histidine R Group Buffer System
Histidine is an amino acid that helps to protein synthesis. Normally amino acids can act as a buffer because they have -OH and -NH2 sides. At this time I’m not going to write about that because that is a very ordinary thing.
Histidine has a special buffer ability in its R group. Usually, the R group of amino acids not having the buffering ability. That’s why this is a special case.
Now I’ll do my explanation action using this image.
When ph=0
This is a very very acidic ph value. Now see my highlighted parts on the image above ph value. Both -NH2 groups have taken H+ to control H+ concentration.
When ph=4
You can see in this time two -NH2 groups are in the same condition as before. But the acidity is not greater than before so, -COOH group doesn’t need to bear an H+.
When ph = 8
By the acidity of this solution is lesser than before 2 times. Therefore only one -NH2 is bearing an H+. Rest -NH2 and -COOH are free of H+s.
When ph = 12
This is not an acidic solution at all. This is strongly based. You can see any group of the above is not binding with H+s. All of them are free from H+.
So this special group called Imidazole Functional Group. I think now your problem is over. This is how the R group of Histidine acts as a buffer.