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Hi,
So glycine has a pI of approximately 5.5 (NH3+ group has a pKa of ~9 and COOH of ~2). If another amino acid that has an OH somewhere in its side chain with a pKa of ~9, would its pI be lower or higher than that of glycine? Seems pretty easy but here is where I get confused; the OH does not have a charge on it and would first act as an acid so I thought it's pI would be lower. However, apparently the pI is greater since to calculate it, we average all the pKas. However, that would be the case if the side chain was OH2+, right? Can anyone follow where I'm coming from?
Thanks.
So glycine has a pI of approximately 5.5 (NH3+ group has a pKa of ~9 and COOH of ~2). If another amino acid that has an OH somewhere in its side chain with a pKa of ~9, would its pI be lower or higher than that of glycine? Seems pretty easy but here is where I get confused; the OH does not have a charge on it and would first act as an acid so I thought it's pI would be lower. However, apparently the pI is greater since to calculate it, we average all the pKas. However, that would be the case if the side chain was OH2+, right? Can anyone follow where I'm coming from?
Thanks.