HEMATIN COMPOUNDS IX FHOTOMETAHOLTSM 



151 



in air with cytochrome c oxidase and catalytic amounts of cytochrome 

 c. 



The other chloroplast hematin compound is a "6" type cytochrome, 

 called 5g by Hill (14). This hematin compound appears to be asso- 

 ciated with the chloroplasts of a variety of plants. Like cytochrome 

 /, it is bound in the chloroplast structure firmly enough to withstand 

 extraction bj'' aqueous solvents. 



Cytochrome / and cytochrome b& cover a range of redox potential 

 which is more than half of the total required to span the difference 

 between the hydrogen and oxygen electrodes at physiological pH 

 (14). Thus, these two compounds provide the chloroplast with an 

 electron transfer system which, in principle, could carry out oxida- 

 tions in either direction over a large fraction of the physiological range. 



HEMATIN COMPOUNDS OF FACULTATIVE PHOTO SYNTHETIC 



BACTERIA 



The nonsulfur purple bacteria are classified at present into two 

 genera, Rhodospirillum and Rhodopseudomonas (35). Representative 

 species contain large amounts of soluble hematin compounds which 

 can be described as modified "c" cytochromes (19). Like cytochrome 

 /, all these heme proteins show high positive redox potentials. Again 

 like cytochrome /, thej^ are not substrates for a cytochrome a type 

 oxidase, and they can be coupled nonenz\^matically with cyto- 

 chrome c. 



The heme protein from R. ruhrum has been studied most inten- 



TABLE I. Some Properties of R. rubrum-Cytochxome c Compared with Mam- 

 malian Cytochrome c (38) 



R. rubrum-cytocYiTOTne c 



Mammalian cytochrome c 



Classification 

 Stability 



Modified c 



Resistant to extremes of 



heat and acidity 

 None 

 None 



Autoxidation 



Reaction with CO on reduc- 

 tion 



Isoelectric point (pH) 



Electrophoretic mobility pH Cathodic, 3.1 X 10 ~* 

 7 (cm.Vvolt-sec.) 



Absorption on IRC-50, pH 7 None 



Approximately 7 



Standard c 



Resistant to extremes of 



heat and acidity 

 None 

 None 



10 



Cathodic, 8.2 X 10"' 



Stronglj- absorbed 



