Metal mercaptide linkages

A. In vitro Metallothionein/Na AuTM Reactions. Highly purified equine renal MT was allowed—to react with various amounts of Na2AuTM and then fractionated on Sephadex 6-50 to separate the protefn-bound and free metals. Because the protein does not have any UV-visible chromophores independent of the metal mercaptide linkages, the protein was "quantitated" by its cadmium content (measured by atomic absorption spectroscopy) and results are reported for various Au/Cd ratios of the reactants. Aliquots of a reaction mixture having a 10/1 Au/Cd ratio were fractionated after 2, 24 and 48 hours incubation time to insure complete reaction. 

B. The DTNB Reaction of Metallothionein. The appearance of reactive (or "free") thiols in the 10,000 Dalton peak of rat renal cytosol, which was previously reported, was apparently inconsistent with the published properties of equine renal metallothionein—namely, that all sulfhydryl groups were present as metal mercaptide linkages. We have subsequently examined the reaction of 5,5 -dithiobis(2-nitrobenzoic) acid (DTNB, a standard agent for measurement of the SH concentrations ( )) with Zn-thionein. A bi-phasic reaction was found in which each step had DTNB dependent kr = 0.41 M", sec ... 

Sulfur in some polysulfide compounds has a significant effect on the cure rate (Table VII) generally resulting in tougher, more resilient materials since the sulfur converts metal mercaptides to disulfide linkages. 

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