O-acetyl serine has the following structure:

O OII II
C—C—O—C—C—C—OHINH2
It can can be hydrolyzed to acetic acid and serine by O-acetyl serine acetylase.

A reactio mixture containing 20 mM O-acetly serine, 50 mM NaCl, 50 mM HEPES buffer (pH 7.6), and O-acetyl serine is incubated at 37 C until the O-acetyl serine is completely hydrolyzed. What is the pH of the mixture at the end of the reaction? (For O-acetyl serine, pKa1= 1.9, pKa2= 8.6; for serine, pKa1= 2.2, pKa2= 9.2; for acetic acid pKa1= 4.76; for HEPES, pKa1=3, pKa2= 7.6)