Haemoprotein of Purple Photosynthetic Bacteria 



421 



cited in this table contain detailed descriptions of methods used. It will be 

 seen, not only in connection with these particular properties but with others 

 discussed later, that RHP's vary somewhat in detailed physical nature. 

 However, the variation is not more than that encountered in other estabhshed 

 categories of haematin compounds, such as cytochromes of the c type, b type, 

 haemoglobins, etc. 



Table 1. Physical properties of rhp* 



(Cf. Newton and Kamen. 1956; Bartsch and Kamen, 1958) 



* Values in this table corrected in proof; see Horio and Kamen, 1960. 



t C.G.S. units. 



% Electrophoretic mobilities at other pH and ionic strengths are 

 omitted. See original references cited above. 



§ Electrometric titration shows that oxidation-reduction of RHP is 

 reversible and involves a one-electron change. 



Chemical Properties 



The chemical behaviour of RHP has been studied mainly using the R. 

 rubrum preparation, but recent studies (Bartsch and Kamen, 1960) have 

 shown that results obtained with this preparation are duplicated in every 

 detail using the Chromatium RHP. We shall summarize here the chemical 

 properties most relevant for the present discussion. 



RHP is soluble in water. It appears to have minimal solubility below 

 pH 5, as is expected from its isoelectric point. In general, it salts out with 

 ammonium sulphate at concentrations which differ slightly from those 

 effective with the corresponding cytochrome c protein obtained from the same 

 source. However, RHP shows solubility behaviour so much like cytochrome 

 c that it is advantageous to devise extraction procedures which minimize 

 contamination with cytochrome c before commencing extensive fractionation 

 of RHP (Bartsch and Kamen, 1958). 



RHP resembles mammalian cytochrome c in heat stability and resistance 

 to denaturation by acid or base. However, at strongly alkaline pH (greater 

 than 1 1), RHP undergoes a reversible denaturation in which it assumes the 

 spectrochemical form of a haemochrome hke cytochrome c, with char- 

 acteristic triply-banded spectra in oxidized and reduced forms. The original 



