Kinetic studies on the reaction between native globin and haem derivatives

Abstract

Proto-, meso-and deutero-haematin react with human globin at a rate determined by the properties of the haematin. Carboxyprotohaem reacts rapidly with globin. An intermediate reversible complex is formed with combination and dissociation velocity constants of 5 X 107 M-1 sec.-1 and 1700 sec.-1 respectively at pH 9. 1 and 19[degree]. The complex is converted into carboxyhaemoglobin in a first-order process with rate constant 370 sec.-1 at 19[degree] and pH 9. 1. The activation energy is 12 kcal. The effects of pH, viscosity and temperature on the reaction of carboxyhaem with globin have been examined. Similar results have been obtained with monocyanide haem both by following the direct reaction and by observing the rate of replacement of cyanide in dicyanide haemoglobin by globin.