Lanthanide ions induce hydrolysis of hemoglobin-bound 2,3-diphosphoglycerate (2,3-DPG), conformational changes of globin and bidirectional changes of 2,3-DPG-hemoglobin's oxygen affinity.
The changes in structure and function of 2,3-diphosphoglycerate-hemoglobin (2,3-DPG-Hb) induced by Ln(3+) binding were studied by spectroscopic methods. The binding of lanthanide cations to 2,3-DPG is prior to that to Hb. Ln(3+) binding causes the hydrolysis of either one from the two phosphomonoester bonds in 2,3-DPG non-specifically. The results using the ultrafiltration method indicate that Ln(3+) binding sites for Hb can be classified into three categories: i.e. positive cooperative sites (N(I)), non-cooperative strong sites (N(S)) and non-cooperative weak sites (N(W)) with binding constants in decreasing order: K(I)>K(S)>K(W). The total number of binding sites amounts to about 65 per Hb tetramer. Information on reaction kinetics was obtained from the change of intrinsic fluorescence in Hb monitored by stopped-flow fluorometry. Fluctuation of fluorescence dependent on Ln(3+) concentration and temperature was observed and can be attributed to the successive conformational changes induced by Ln(3+) binding. The results also reveal the bidirectional changes of the oxygen affinity of Hb in the dependence on Ln(3+) concentration. At the range of [Ln(3+)]/[Hb]<2, the marked increase of oxygen affinity (P(50) decrease) with the Ln(3+) concentration can be attributed to the hydrolysis of 2,3-DPG, while the slight rebound of oxygen affinity in higher Ln(3+) concentration can be interpreted by the transition to the T-state of the Hb tetramer induced by Ln(3+) binding. This was indicated by the changes in secondary structure characterized by the decrease of alpha-helix content.
Cheng
Y
Y
National Research Laboratories of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, People's Republic of China.
Lin
H
H
Xue
D
D
Li
R
R
Wang
K
K
D019794:2,3-Diphosphoglycerate / Q000737:chemistry*; D002412:Cations; D005453:Fluorescence; D006454:Hemoglobins / Q000737:chemistry; D006801:Humans; D006868:Hydrolysis; D009682:Magnetic Resonance Spectroscopy; D008674:Metals, Rare Earth / Q000494:pharmacology*; D008956:Models, Chemical; D008968:Molecular Conformation; D010100:Oxygen / Q000737:chemistry*; D011221:Praseodymium / Q000494:pharmacology; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D013725:Terbium / Q000494:pharmacology
D002412:Cations; D006454:Hemoglobins; D008674:Metals, Rare Earth; D013725:Terbium; D019794:2,3-Diphosphoglycerate; C100003:deoxyhemoglobin; D011221:Praseodymium; D010100:Oxygen