can be assigned to the /3E11 valine methyls. The spectra of isolated a and ß chains indicate the a-and /3-chain con-

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Nuclear magnetic resonance studies of the contact-shifted spectra of heme protons in deoxyhemoglobin A from human adults show conclusively that oxygen binds to the a hemes in preference to the fi hemes. (9). Perutz further describes how 2,3-diphosphoglycerate(P2 glycerate) and hydrogen ion inhibit-the structural transition from the deoxy to the oxy quaternary structure (9). Based on indirect kinetic and spectroscopic evidence, Gray and Gibson (10) have proposed that CO combines first with the fi chains before the a chains. As yet, there is no direct experimental evidence showing that oxygen binds to one type of heme in Rb A in preference to another. This is a preliminary report on the preferential binding of oxygen to the a-chain hemes in the presence of P2 glycerate or inositol hexaphosphate(1P6), as monitored by selective decrease of the contact-shifted resonances of the a chains. MATERIALS AND METHODSHbCO A was prepared (11)

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