Sulfhydryls blocking agents

Since ANTU is a sulfhydryl blocking agent, cysteine has been tried in rats and was effective in some cases. There is no human experience with cysteine and its use is not recommended. 

Methyl methanethiosulfonate (MMTS) is a small reversible blocking agent for sulfhydryl groups (Thermo Fisher, Toronto Research). It reacts with free thiols to form a dithiomethane modification with release of sulfinic acid (Figure 1.122). The sulfinic acid component decomposes into volatile products, which don t affect the disulfide formed from the MMTS reaction Alkylthiosulfonates react rapidly with thiols under mild conditions at physiological pH. The MMTS compound is a liquid at 10.6 M concentration and is conveniently added to a reaction medium by pipette. Complete thiol modifications of available cysteine residues in proteins can... 

Latent forms of MMPs can be activated by mechanisms which cause the dissociation of the intramolecular complex between a particular cysteine residue and the required zinc metal ligand (a complex that blocks the active site) [47], This occurs because the cysteine of the latent enzyme is coordinated to the active site in a particular way that blocks the MMP active site. Collectively, the activation of MMPs occurs through a process which has been termed the cysteine-switch . Activators of the MMPs include proteases (e.g. plasmin), conformational perturbants (SDS, NaSCN), heavy metals and organomercurials (e.g. Au(I) compounds, Hg(II)), oxidants (e.g. OC1-), disulfide compounds (e.g. GSSG) and sulfhydryl alkylating agents (e.g. V-ethylmaleimide) [47 and refs, therein]. 

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