Abstract
Abstract The pH-dependent transitions and the thermal unfolding of defatted human serum albumin in 0.2 m KCl as followed by polarimetry at 233 nm are found to be independent processes. The apparent net loss of structure (α helix) in the unfolding between pH 7 and 9 is 2.5%, in the N-F transformation it is 8% and in the acid expansion 1%. The two last mentioned transitions seem to be independent of each other. There is a temperature of maximum stability of the N stage in the N-F transformation at 18°. The thermal unfolding and the unfolding by guanidine hydrochloride at pH 2.6 both are continuous processes of apparently low cooperativity with no distinct intermediates. The temperature of maximum stability (Tmax) of human serum albumin is at all pH values below 0°, furthermore it is found to vary continuously with the concentration of guanidine hydrochloride, and in 0.2 m KCl at pH 2.6, Tmax can be extrapolated to -6°. From the transition profiles for thermal denaturation, the three dimensional structure of human serum albumin might be pictured to consist of segments of helical configuration with differential stabilities toward denaturation which impart the ability to unfold simultaneously, but more or less independently.
Highlights
From the transition profiles for thermal denaturation, the three dimensional structure of human serum albumin might be pictured to consist of segments of helical configuration with differential stabilities toward denaturation which impart the ability to unfold simultaneously, but more or less independently
For I
Human serum albumin was obtained from Behringwcrke (Lot 3142)
Summary
The pH-dependent transitions and the thermal unfolding of defatted human serum albumin in 0.2 M KC1 as followed by polarimetry at 233 nm are found to be independent processes. From the transition profiles for thermal denaturation, the three dimensional structure of human serum albumin might be pictured to consist of segments of helical configuration with differential stabilities toward denaturation which impart the ability to unfold simultaneously, but more or less independently. The electrophoretic mobility of bovine serum albumin has been determined [6], and titration curves have been obtained [7] at t\vo different temperatures. No such data are available for human serum albumin. The acid transformations and the transition between pH 7 and 9 have been followed by polarimetry at 313 nm for both HSAl [2, 3] and bovine serum albumin [2, 3, 8], but only
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