FUNCTIONAL PROPERTIES OF A HEMOGLOBIN CARRYING HEME ONLY ON ALPHA CHAINS

The functional properties of a hemoglobin carrying heme only on the α chains (αhβ) are described. The protein shows nearly hyperbolic oxygen equilibrium curves with three to ten times higher oxygen affinity than normal hemoglobin, depending on pH. The Bohr effect is present, but is about one-half that of normal hemoglobin. The velocity constant of the reaction between ahβ and CO is much higher than in hemoglobin (initial second-order rate constant, 1′ ≃ 2 × 106 m-1 sec-1); the same kinetic pattern is obtained in rapid mixing and flash photolysis experiments. Addition of the full heme complement to the αhβ compound gives a product with all the properties of natural hemoglobin both in respect to the O2 equilibrium and to the kinetics of reaction with CO. The functional properties of the αhβ compound are different from those of isolated α chains, which indicates that the reactivity of the heme in a given chain is modified by interaction with the partner chain, even if the latter is devoid of prosthetic group. © 1968, American Chemical Society. All rights reserved.