Spectrophotometric Titration of Ferredoxins and Chromatium High Potential Iron Protein with Sodium Dithionite

Ferredoxins from Closfridium pasfeurianum, Closfridium acidi urici, Pepfosfrepfococcus elsdenii, spinach, and parsley, and high potential iron protein from Chromafium were titrated to full reduction with sodium dithionite.The changes in the spectra showed that the bacterial ferredoxins accepted two reducing equivalents; the plant ferredoxins and high potential iron protein accepted only one reducing equivalent.The titration curves for the bacterial ferredoxins and parsley ferredoxin showed a variable lag phase during which there was no net loss in absorption.When C. acidi urici and C. pasfeurianum ferredoxins were titrated with dithionite in the presence of 2,2'-bipyridyl, the iron complex tris-(Z,Z'-bipyridyl)-Fe@) was formed during the lag phase, suggesting that in this part of a titration contaminating ferric iron was reduced to ferrous iron.