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The Ligand-binding Properties of desHis(146β) Hemoglobin

1973; Elsevier BV; Volume: 248; Issue: 18 Linguagem: Inglês

10.1016/s0021-9258(19)43458-3

1083-351X

Keith Moffat, John S. Olson, Quentin Gibson, John V. Kilmartin,

Neonatal Health and Biochemistry

Abstract DesHis (146β) hemoglobin is a β chain modification of human hemoglobin in which the COOH-terminal histidine 146β has been removed by digestion with carboxypeptidase B. Previous crystallographic investigations of the structures of desHis deoxyhemoglobin and deoxyhemoglobin Hiroshima (His 146β → Asp) suggest that the atomic structures of these derivatives differ from each other and from hemoglobin A only in the immediate environment of the COOH-terminal residue. Kinetic studies of the binding of oxygen, carbon monoxide, and n-butyl isocyanide to desHis hemoglobin reveal that the properties of desHis hemoglobin and hemoglobin Hiroshima are indeed similar, but not identical; the properties of both differ appreciably from those of hemoglobin A. These qualitative differences in kinetic properties are not readily reconciled with the apparently minor structural differences revealed in the structural studies. They suggest rather that the unliganded forms of both derivatives adopt a new conformation, or series of conformations in slow equilibrium, which are distinct from the conformations of either deoxy- or oxyhemoglobin A.