Binding of heme-CO to bovine and porcine beta-lactoglobulins.
Two molecules of heme-CO bind to bovine or porcine beta-lactoglobulin (BLG) with an average affinity of 0.5 microM. The affinity increases with pH, with a transition near pH 7.5, indicating a conformational change in the protein. Heme-CO does not bind to the predominantly alpha-helix conformation of BLG, which occurs in solutions with more than 40% ethanol or methanol. Fluorescence energy transfer measurements have been made for the complex of BLG with retinol and/or heme-CO. Two species of BLG were used. While bovine BLG possesses two tryptophans (at positions 19 and 61) which are quenched by about a factor of 2 by either retinol or heme-CO, the porcine species has only one tryptophan (at position 19) whose fluorescence is decreased by a factor of 15 when both hemes are bound, indicating that at least one of the heme-binding sites is near (< 20 A) to this tryptophan. The fluorescence of retinol (complexed to BLG) is also quenched by the addition of heme-CO, indicating that BLG can bind both molecules simultaneously; a separation of 25 A between retinol and heme was calculated. The results suggest at least two hydrophobic pockets for this protein.
Marden
M C
MC
INSERM U299, Hôpital de Bicêtre, Le Kremlin Bicêtre, France.
Dufour
E
E
Christova
P
P
Huang
Y
Y
Leclerc-L'Hostis
E
E
Haertlé
T
T
D000818:Animals; D002248:Carbon Monoxide / Q000378:metabolism*; D002417:Cattle; D004735:Energy Transfer; D006418:Heme / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007782:Lactoglobulins / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry; D013552:Swine
D007782:Lactoglobulins; D006418:Heme; D002248:Carbon Monoxide