Haemoprotein of Purple Photosynthctic Bacteria 431 



cytochromes. From the long-range view we feel it is probably best to avoid 

 addition of yet another letter group to the thi-ee already in existence, especially 

 when it is considered that RHP and its presumed analogues among the non- 

 photosynthetic bacteria may be only structural variants of cytochrome c. 

 Whatever terminology is adopted, it should be sufficiently flexible to include 

 not only RHP, which represents a myoglobin-type haematin compound, but 

 also other kinds of cytochrome variants which are possible on the basis of 

 present concepts of haemoprotein structure. 



ADDENDUM 

 Further studies have required some revision of results as originally re- 

 ported at the Symposium. The improved values (Horio and Kamen, 1960) 

 have been incorporated in Tables 1 and 2. It has also been found (Horio and 

 Kamen, 1960) that the minimum molecular weight of the R. rubrum prepara- 

 tion is 12,900 (based on iron estimation) and 13,000 (based on estimation of 

 pyridine haemochrome). The molecular weights of R. rubrum RHP and of 

 Chromatium RHP as determined by physical methods have been found to be 

 26,000 and 36,000 respectively. The corresponding minimum molecular 

 weights, as indicated by estimation of pyridine haemochrome and of iron 

 content are 12,900 and about 17,000 respectively. Thus there appear to be 

 two haem moieties per mole of RHP in both preparations. 



A ckno wledgemen ts 



Much of the early work on which this report is based was made possible 

 by the financial support of the C. F. Kettering Foundation and by the Linde 

 Air Products Company. Continued support throughout the later period of 

 the research has come from the National Science Foundation and the National 

 Institutes of Health, whose help we gratefully acknowledge. Permission to 

 reproduce Figs. 1, 2, 4 and 5 has been graciously extended by the Editor of 

 the Journal of Biological Chemistry. 



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