The binding of hydrogen ions to an acidic glycoprotein from bovine cortical bone

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Abstract
The H+ion dissociation of bone sialoprotein in 0.2 M-NaCl at 25[degree] was studied. The total content of carboxyl groups available for titration was calculated by comparing the titration curve with the titration curves of 3 model systems and by the use of analytical data. This comparison showed that 7.0 carboxyl groups/mol. do not participate in the titration, and it is proposed that these are aspartic acid or glutamic acid carboxyl groups present as amides; this is also indicated by titration of the sialoprotein after acid hydrolysis. The titration of carboxyl groups was found to agree well with the Linderstrom-Lang equation for spherical macroions.