Mechanism of rhodanese action: isotopic tracer studies.

In a previous publication (2) a double displacement mechanism for the catalytic activity of rhodanese (thiosulfate cyanide sulfurtransferase) was proposed on the basis of polarographic evidence. In addition it was concluded from the polarographic data that crystahine beef liver rhodanese is an enzyme-substrate intermediate containing two activated substrate sulfur atoms per molecule. This communication reports the results of sulfur-35 tracer experiments which support the previous conclusions. The splitting of labeled thiosmfate and the specific binding of the transferable sulfur atom by rhodanese have been demonstrated. Studies on the removal of the substrate sulfur from the enzyme have provided some additional data concerning the nature of this enzyme-substrate intermediate.