Study of The Conformation Changes of Blood Serum

Abstract

pH and conductometric titration of blood serum (Goat's) in 5%
aqueous medium gave two inflexions and the corresponding two
breaks with N/20 HCI and only one inflexionlbreak with N/20
NaOH solution. In 0.25 M KCI there was only one inflexion in both
acid and alkali. In 8 M urea solution the number of inflexionlbreaks
rose to three. The coulombic interactions between oppositely
charged sities in the protein chain seems to have screened, at least
in part by a neutral salt like KCI present in large concentration as
also shown by the fact that the fall of pH by the addition of (5 mL)
of acid is more in aqueous medium than in KCI solution.
Urea being a powerful disruptor of hydrogen bond the protein
chain would, in all probability, exist as a random coil conformation
and the study of pH titration curves revealed the acidic and basic
groups having three step reactions in it. The nature of the titration
curve is also altered in urea solution. The initial pH of blood serum
rose from 7.2 to 7.9 showing there by the protons of the NH₃ cations
in the zwitter ions be irnmobilised by hydrogen bond formation
with urea as suggested by Donovan, Laskowski and Scherage. Expansion
of the protein random coil in the denatured form also seems
to occur in the pH titration.