Haemoprotcin of Purple Photosynthetic Bacteria 423 



/^-carbons of the pyrrole moieties of porphyrins and metalloporphyrins. These 

 support the suggestion (Bartsch and Kamen, 1958) that the protein presents 

 an electronegative group, such as carboxyl, to the central iron atom of the 

 haem (see also, Williams, this Symposium, p. 41 ) and that it is this functional 

 grouping (possibly as part of a long chain) which prevents approach of a 

 basic co-ordinating group. It will be of great interest to attempt isolation of 

 a haem peptide from RHP and if successful, to ascertain its structure. 



Immunochemical Properties 



All of the haemoproteins, including the RHP type, derived from either 

 R. rubrum or Chromatium, can function as antigens, evoking characteristic 

 antibody synthesis in rabbit sera. The antibody against any one haemo- 

 protcin, when tested by the Ouchterlony technique, by precipitation, by 

 complement fixation, etc., does not appear to interact with any other haemo- 

 protein, whether of a different type from the same bacterium or of the same 

 type from a different bacterium. For example, the anti-RHP of Chromatium 

 will not interact with the R. rubrum RHP, nor with cytochrome c from either 

 Chromatium or R. rubrum. Thus, there are strain differences in RHP from 

 different sources, just as there are in the haemoglobins and myoglobins. 



The antigenic properties of RHP preparations afford a means for applying 

 immunochemical techniques as aids in structure determination, and also as 

 a basis for monitoring denaturation during extraction. 



Spectroscopic Properties 



In Figs. 1 to 5, characteristic features of the absorption spectra under 

 various conditions are exhibited. The main properties may be summarized 

 as follows. 



1. Spectra of the oxidized and reduced forms (Figs. 1-3) resemble those 

 for a myoglobin pigment, except for a general sliift of all absorption 

 maxima toward shorter wavelengths than those found for myoglobin or 

 peroxidase. Tliis shift accords with the apparent mesohaem character of the 

 prosthetic group of RHP. 



2. There is a characteristic haematin band at 630-640 m^ which dis- 

 appears on reduction and reappears on oxidation. This band is used for 

 preliminary monitoring of extracts for the presence of RHP. 



3. The Soret band of the reduced form is complex, showing a persistent 

 shoulder some 5-10 m/^ on the long wavelength side of the maximum absorp- 

 tion at 423-426 m^. There appears to be a more pronounced shoulder in the 

 R. rubrum compound (Fig. 1) than in the Chromatium compound (Fig. 3). 



4. Carbon monoxide forms a complex with reduced RHP, showing a 

 typical haemochrome spectrum (Fig. 5). As compared with unreacted 

 reduced RHP, the Soret peak of the complex RHP sharpens, intensifies, and 



