What is glycine's isoelectric point (pI)?

Glycine is an amino acid that has a unique structure with both an amino group and a carboxyl group, which means it can exist in different protonation states depending on the pH of the solution. The isoelectric point (pI) of an amino acid is the pH at which the molecule has no net charge, meaning that the positive and negative charges balance each other out.

For glycine, the pI can be calculated using the pKa values of its functional groups. Glycine has a pKa value for its carboxyl group (approximately 2.35) and a pKa value for its amino group (approximately 9.78). The pI is determined by averaging these two pKa values because the side chain of glycine is neutral and does not contribute any additional pKa.

The calculation for glycine's pI is performed as follows:

pI = (pKa1 + pKa2) / 2 = (2.35 + 9.78) / 2 = 6.07.

This value is often rounded to 6.01 in various biochemistry contexts to reflect typical values encountered in literature. Therefore, option B, with a pI of 6