CRYSTALS OF HEMOGLOBIN WITH THE T-QUARTERNARY STRUCTURE BIND OXYGEN NONCOOPERATIVELY WITH NO BOHR EFFECT

被引:118
作者
MOZZARELLI, A [1 ]
RIVETTI, C [1 ]
ROSSI, GL [1 ]
HENRY, ER [1 ]
EATON, WA [1 ]
机构
[1] NIDDKD,CHEM PHYS LAB,BETHESDA,MD 20892
关键词
D O I
10.1038/351416a0
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
THE relationship between the structure and function of haemoglobin has mainly been studied by comparing its X-ray crystal structures with its function in solutions 1-11. To make a direct comparison we have studied the functional properties of haemoglobin in single crystals, an approach that has been an important part of the investigation of several enzyme mechanisms 12, 13. Here we report on the oxygen binding by single crystals of human haemoglobin grown in solutions of polyethylene glycol. Unlike haemoglobin crystals formed in concentrated salt solution, which crack and become disordered on oxygenation 14-16, crystals grown in polyethylene glycol remain intact. X-ray studies have shown that the T (deoxy) quaternary structure of haemoglobin in this crystal at pH 7.0 is maintained at atmospheric oxygen pressure, and that the salt-bridges are not broken 17-19. We find striking differences between oxygen binding by haemoglobin in this crystal and by haemoglobin in solution. Not only is oxygenation of the crystal noncooperative, but the oxygen affinity is independent of pH in the range 6.0-8.5, and is much lower than that of the T state in solution. The lack of cooperativity without a change in quaternary structure is predicted by the two-state allosteric model of Monod, Wyman and Changeux 1, 5. The absence of a Bohr effect without breakage of salt-bridges is predicted by Perutz's stereochemical mechanism 2, 4, 9-11. In contrast to the X-ray result that oxygen binds only to the alpha-haems, our measurements show that the alpha-haems have only a slightly higher affinity than the beta-haems.
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页码:416 / 419
页数:4
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