324 ELECTRON TRANSPORT 



tion bands which would make direct observation feasible. Added iron 

 protein can reduce chromatophore cytochrome (s), which can then under- 

 go light-induced changes. Interaction of reduced iron protein with 

 photooxidized particle cytochrome would result in the observed anaero- 

 bic photooxidation of the iron protein. No evidence was obtained as to 

 the nature of the reductant which seems to accumulate as the iron 

 protein is photooxidized and then reduces the oxidized iron protein in 

 the dark. 



There are similarities between properties of Chromatium iron 

 protein and the PPNR and ferredoxin types of iron- containing proteins; 

 here are emphasized some differences which may indicate that the 

 two types of proteins are functionally different. A primary difference 

 is the widely separated oxidation- reduction levels at which the proteins 

 appear to function, E^ for ferredoxins and PPNR is reported to be 

 -0,42 volt (8), whereas Chromatium iron protein seems to operate at 

 Ern = +0,35 volt. If this discrepancy is substantiated by further in- 

 vestigation, then the two kinds of proteins must perform different 

 functions. 



The ferredoxin type proteins are more strongly adsorbed by DEAE- 

 cellulose (6-8) than is the Chromatium protein and they require 4-5 

 times higher salt concentration for elution from the adsorbent. This 

 difference in acidic properties of the proteins may merely reflect a 

 difference in charged amino acid content, or may indicate that some 

 major difference in chemical constitution exists between the two kinds 

 of proteins. 



Drs. H. Mower and J. E. Carnahan reported in a private communi- 

 cation that Chromatium iron protein showed less than 1 per cent the 

 activity of a comparable amount of authentic ferredoxin when tested in 

 the C. pasteuriaimm pyruvate phosphoroclastic assay for ferredoxin 

 (6). The iron protein is either a ferredoxin with quite different specif- 

 icity from the clostridial protein or it is contaminated with a small 

 amount of an effective ferredoxin. A definitive test for ferredoxin 

 function would involve a reversible oxidation- reduction reaction be- 

 tween the iron protein and the homologous Chromatium hydrogenase. 

 An assay based on this principle has not been attempted. 



Chromatium iron protein contains a chromophore in addition to the 

 iron. Inasmuch as the spectra of the iron protein resemble reported 

 spectra of ferredoxins and PPNR (8), the latter types of proteins may 

 contain a functional group similar to the fluorescent chromophoric 

 substance found in the Chromatium protein. 



An estimate may be made of the minimum molecular weight of the 

 complex iron protein. If all the iron found in the protein is functional, 

 then a molecule containing only 3 Fe would be too small, but one with 

 4 Fe (MW = 4 X 55.5/0.02 - 11, 100 g/mole) could easily accommodate 

 the minimum peptide of approximately 8900 MW, plus iron and chromo- 

 phore material. 



