Haemopiolein of Purple Photosynthetic Bacteria 



435 



because of the optical artifacts caused by the flow of the spirillum in the observation 

 tube. A similar study with Chromatiuin gives satisfactory results, but the oxidation 

 of the cytochromes is very slow. 



3,2>jM 

 Oxygen 



554-540m>i 



log I0/I-O.OOI5 l6jjM 



5 10 



Time after flow stops 

 (sec) 



50 



Time after flow stops (sec.) 



Fig. 3. Rapid flow studies of the speed of oxidation of cytochrome of type 

 c by cytochrome o in M. pyogenes var. albus (left) and A. suboxydans (right). 



On the Oxidase Function of RHP 



Smith : In regard to the oxidase function of the RHP of Rhodospirilluin rubrum, as dis- 

 cussed by Kamen, we have not been able to find any respiratory activity in isolated 

 chromotophores of these organisms, although other fractions of the broken-cell 

 suspensions can respire. Also we cannot find any evidence for the formation of the 

 CO-compound of reduced RHP in anaerobic suspensions of R. rubrum that have been 

 grown in the dark with aeration, although they respire very rapidly. Finally, an 

 oxidase function for RHP is very puzzling in Chromatium, since it is an obligate 

 anaerobe. 



Kamen: We have noted that RHP could hardly function as an oxidase in Chromatium. 

 In fact we regard it as likely that the protein in R. rubrum and other facultative 

 bacteria may function as an oxidase whereas in Cluomatium it may retain only an 

 electron-transferring property. Another uncertainty relates to the fact that cyanide 

 inhibits R. rubrum respiration whereas there is no spectroscopic evidence of 

 combination between RHP and cyanide. However, this also appears to be the case 

 with Pseudomonas oxidase (as reported by Horio et al., this volume, p. 302) where 

 cyanide inhibits without showing visible alterations in the pigment spectrum. As for 

 the experiments on R. rubrum grown in the dark, it would be a matter of great difficulty 

 to interpret results of such an approach. We know there are profound changes in 

 haematin enzyme content with such culture conditions and that not only RHP, but 

 also catalase, peroxidase and the various cytochromes fluctuate greatly. At present, 

 there are no compelling reasons for discarding the oxidase hypothesis. 



Addendum (in proof). Horio, working in Chance's laboratory with Dr. C. P. S. 

 Taylor, has now found (September, 1960) that the CO-action spectrum for oxidase 

 activity in dark-grown aerobic R. rubrum is identical with the CO-reduced RHP 

 spectrum. 



