Aromatic amino-acids and subunit assembly in the hemoglobins from Scapharca inaequivalvis: a fluorescence and CD study of the apoproteins.
The dimeric and tetrameric hemoglobins from the mollusc Scapharca inaequivalvis have a unique assembly that places the heme-carrying E and F helices in the inside of the molecule. These helices form the intersubunit contact in the dimer, which represents the structural unit since the tetramer is a dimer of dimers. The E and F helices are highly conserved and contain about 70% of the phenylalanine and tyrosine residues, while the tryptophan residues are near the tetramer contact. The spectroscopic properties (circular dichroism and intrinsic fluorescence) of the aromatic amino-acid residues in the two globins indicate that heme removal brings about a larger conformational change in the tetrameric than in the dimeric protein and that the tryptophan residues acquire a more rigid conformation in the tetramer.
Verzili
D
D
Department of Biochemical Sciences, University La Sapienza, Rome, Italy.
Rosato
N
N
Ascoli
F
F
Chiancone
E
E
D000818:Animals; D001059:Apoproteins / Q000032:analysis; D002942:Circular Dichroism; D006454:Hemoglobins / Q000032:analysis; D008974:Mollusca / Q000032:analysis*; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence
D001059:Apoproteins; D006454:Hemoglobins