HAEM PROTEIN CONTENT AND FUNCTION IN RELATION TO STRUCTURE 289 



chemical process. There are abundant data showing that in Chyomotium 

 [36] and in R. rubriim [:;4] the primary oxidation involves the cytochrome 

 c-type haem protein which has been isolated, purified, and characterized 

 in our laboratorv [26, 27]. The evidence includes not only kinetic studies 

 in the presence and absence of a variety of inhibitors, but also the demon- 

 stration that the cvtochrome oxidation involves several components, one 

 of which is oxidized as rapidly at — 180" as at room temperature [35]. 

 Data for comparable changes in oxidation state of chloroplast haem pro- 

 teins remain meagre [^s\. 



Now, it mav be that there are qualitative difi'erences between plant and 

 bacterial photosyntheses, primarily owing to the ability of the former to 

 produce molecular oxygen. There certainly may be factors not considered 

 in the previous discussion, which are of crucial importance in the process 

 of oxygen production. One possibility is the metal, manganese, which is 

 present in very large amounts in chloroplasts, and which appears to be 

 required for green plant photosynthesis, whereas it does not seem essential 

 (at least in more than trace amounts) in bacterial photosynthesis [56]. 

 Kessler has presented some preliminary evidence [57] correlating man- 

 ganese with the oxygen-producing system. Very recently, Treharne, 

 Brown, Eyster, and Tanner [^8] have found that an electron spin resonance 

 arising from manganese ion in Chlorella kept in the dark disappears upon 

 illumination, and that this phenomenon can be linked with a photo- 

 oxidation of A In + -\* 



It is also known from a discovery by the late R. Emerson that two 

 quanta can co-operate over relatively long time intervals to increase the 

 yield of molecular oxvgen. In the chromatophore there is a relatively small 

 ratio of chlorophvU to protein. From Table I we can see the ratio of 

 chlorophvll to cvtochrome is ~ 15. This ratio is usually greater than 

 several hundred in most chloroplasts [15]. Similarly the ratio of chloro- 

 phyll to pyridine nucleotide is 20 in the Chrotnatium chromatophore, 

 whereas it can be no less than 2500 in spinach chloroplasts [59]. This 

 greatlv increased ratio of chlorophyll to other components in oxygen 



* We may recall, if only in a footnote, the remarkable reaction, first noted by 

 R. H. Kenten and P. J. G. Mann in 1949 and studied since by them (see Biocliem. J. 

 45» 255; 46, 67; 52, 125; 6l, 279) in which manganous ion is oxidized photo- 

 chemically in the presence of plant peroxidase, hydroperoxide, and a peroxidase 

 substrate, such as a monohydric phenol. Pyrophosphate is added to trap the 

 manganic ion formed as the insoluble manganic pyrophosphate. These authors 

 have found that chloroplasts can catalyze this reaction, and suggest that in photo- 

 synthesis a cycle occurs involving alternate photo-oxidation of manganous ion to 

 manganic and reduction by plant material of manganic to manganous. W. F. 

 Andreae (see Arch. Biochem. Biophys. 55, 584) has determined that this reaction, 

 which depends on the presence of catalase or peroxidase, can be induced by cataly- 

 tic amounts of a hydrogen donor in the presence of a variety of light sensitizers. 

 He has noted further the nature of hydrogen donors most effective in catalysis. 



VOL. n. — u 



