88 



K. Kaziro and K. Tsushima 



Figure 7 shows the replacement of globin-N by cyanide. As seen from the 

 figure, the reaction of replacement of globin-N by cyanide is competitive. In 

 the case of the benzoate-induced ferrihaemochrome, the replacement by 

 cyanide of the globin-N was found to follow a first order reaction (Fig. 7 (I)). 

 However, globin-N of the completed ferrihaemochrome which v/as formed 



100 



o 



50 



4-5 



3-5 30 



-Iog(KCN), 



20 1-5 



Fig. 7. The formation of cyanide-ferrihaemochrome at different concentrations 

 of cyanide. Absorbancy changes of ferrihaemochrome induced by benzoate 

 (Curve I) or lauryl sulfate (Curve II) in the presence of various concentrations of 

 potassium cyanide were measured at 425 m/< in phosphate buffer, pH 8-0 and at 

 16°. The concentrations of methaemoglobin and sodium benzoate (or lauryl 

 sulfate) were 8-63 x 10"* m and 1-25 m (or 10~^ m), respectively. The curves 

 were calculated by use of the relation which is derived from the following equations: 



/ 



I. cyanide-ferrihaemochrome formation in the presence of benzoate, 



Fe+++ -H CN- ^ Fe+++ + gl.N 



\ \ 



gl.N CN 



II. cyanide-ferrihaemochrome formation in the presence of lauryl sulphate, 



gl.N CN 



Fe+++ + 2CN- ^ Fe+++ + 2 gl.N 



\ \ 



gl.N CN 



(CN)" 

 Cyanide compound formation (%) = 100 x a = — ^^ 



where K is the apparent dissociation constant, (CN) is the concentration of free 



cyanide and n is the number of cyanide ions combining with ferrihaemochrome. 



At curve \n = 1 , at curve II n = 2. 



