On the question of the "labile" sulfide in ferredoxin from Clostridium pasteurianum

Abstract

In the present work attempts are made to characterize the nature of the so-called “labile” sulfide in ferreodoxin from Clostridium pasteurianum. A great uncertainty exists upon the origin of this “labile” sulfide. Therefore the response of oxidized ferredoxin to mercury compounds is tested by titration of SH-groups with p-chloromercuribenzoate at various pH values in the range of 5.0–11.0 and in the presence of the denaturing reagents lauryl pyridinium chloride and sodium dodecyl sulfate: The molar ratio p-chloromercuribenzoate: ferredoxin with n = 9 is the same in the native and denatured protein; so it can be stated, that all SH-groups in the native protein are reactive. In another experiment the total sulfur content of ferredoxin was determined by oxidation to sulfate and flame photometric determination of strontium sulfate. These data indicate that the “labile” sulfide is of amino acid origin, being released from the eysteinyl groups.