MODIFICATION OF THE SECONDARY STRUCTURE 

 OF HAEMOPROTEIN MOLECULES 



By K. Kaziro and K. Tsushima 

 Biochemical Laboratory, Nippon Medical School, Tokyo 



Although the principal functions of haematin enzymes are based on the 

 catalytic property of their central iron, the specific functions of the individual 

 haematin enzymes are determined by their protein structures. This may be 

 exemphfied, for instance, in haemoglobin and cytochrome c. The former 

 combines with molecular oxygen reversibly without activating the combined 

 molecule, the latter functions as an electron carrier but does not react with 

 oxygen. These specific functions are maintained strictly by the native state 

 of the protein moiety. Any modification of the secondary structure of their 

 protein molecules will cause diverse alterations of their essential properties. 

 The present paper is concerned with the relationship between the functions 

 of haemoproteins and their protein structures (Tsushima, 1954a, b; 1956a, b; 

 Tsushima and Kawai, 1956; Tsushima and Miyajima, 1956; Okazaki and 

 Tsushima, 1959; Kikuchi and Tomimura, 1954; Suzuki, Tomimura and 

 Mizutani, 1956; Kajita, 1956a), which were studied mainly with haemoglobin 

 as a model molecule of haematin enzymes. 



Studies were made also on the haemoclirome-forming chemical groups of 

 some haemoproteins after the proteins had been artificially unfolded. This 

 provides a new approach to the significance of the protein moiety of the 

 native haematin enzymes in general. 



RESULTS AND DISCUSSION 

 Haem-haem Interaction and Bohr Ejfect of Haemoglobin in the Presence of Urea 



The well-defined characteristics of haemoglobin in the physiological 

 adaptation to respiration are the Bohr effect and haem-haem interaction. 

 In order to demonstrate the possible interrelationship between these physio- 

 logical characteristics of haemoglobin and its protein structure, we studied 

 the binding reaction of haemoglobin with ethyl isocyanide (EIC) (Warburg, 

 Negelein and Christian, 1929; Russell and Pauling, 1939; St. George and 

 Pauling, 1951) in the presence of urea at a concentration which is high enough 

 to modify the protein structure (Okazaki and Tsushima, 1959). The absorption 

 spectrum of reduced haemoglobin is converted to that of ElC-haemoglobin 



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