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Comparative fluorescence properties of bovine, goat, human and guinea pig alpha lactalbumin. Characterization of the environments of individual tryptophan residues in partially folded conformers.

Authors
  • Sommers, P B
  • Kronman, M J
Type
Published Article
Journal
Biophysical Chemistry
Publisher
Elsevier
Publication Date
Apr 01, 1980
Volume
11
Issue
2
Pages
217–232
Identifiers
PMID: 7370388
Source
Medline
License
Unknown

Abstract

alpha Lactalbumin exists as a partially folded conformer (U form) at acid pH. A second partially folded conformer (H form) is formed above 60 degrees. Comparison of the changes in tryptophan fluorescence which occur on forming U and H for the bovine, goat, human and guinea pig proteins, as well as analysis of fluorescence properties for the bovine protein and an N bromo succinimide derivative of this protein, have made it possible to determine which tryptophan residues give rise to such changes in fluorescence, and to draw a distinction between the molecular structure of the U and H forms of the protein. Trp 28 and 109 in the native state transfer their excitation energy to trp 63 whose fluorescence is quenched by a pair of vicinal disulfide bridges. This process persists in the U form of the protein, but is absent in the H conformer. Most of the change in fluorescence seen in the N in equilibrium with U conversion is due to increase in yield of trp 28, while the changes in fluorescence occurring on formation of the H form are due to exposure of trp 63 and elimination of its quenching and/or excited state transfer from 28 to 109.

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