Sulfhydryl groups masking

Monoclonal antibodies to sulfhydryl-terminated PAMAM dendrimers [9,10] could be bound to sulfhydryl-terminated PAMAM dendrimers under stoichiometric conditions favoring complexes of one antibody to one dendrimer. After binding, the exposed sulfhydryl surface may be derivatized to eliminate SH groups. Antibody and dendrimer complexes are then dissociated and the patterned dendrimers are isolated. Only areas masked by the antibody retain sulfhydryl groups, and can therefore be differentially derivatized (to a gold adduct, or to maleimide-linked macromolecules, for instance). 

Because an analysis for amino acids in an acid hydrolysate of a protein gives no information about the state of that particular amino acid in the original protein, chemical methods that do not distort the conformation of the protein can thus provide information on the state of the side chain of that particular amino acid in the protein in solution or in a crystal state. Thus, poorly reactive (sometimes called masked ) sulfhydryl groups of cysteine show different degrees of reactivity, depending upon the chemical agents used (Table III). 

Maleic acid is a linear four carbon molecule with carboxylate groups on both ends and a double bond between the central carbon atoms. The anhydride of maleic acid is a cyclic molecule containing five atoms. Although the reactivity of maleic anhydride is similar to other cyclic anhydrides, the products of maleylation are much more unstable toward hydrolysis, and the site of unsaturation lends itself to additional side reactions. Acylation products of amino groups with maleic anhydride are stable at neutral pH and above, but they readily hydrolyze at acid pH values around pH 3.5 (Butler et al., 1967). Maleylation of sulfhydryls and the phe-nolate of tyrosine are even more sensitive to hydrolysis. Thus, maleic anhydride is an excellent reversible blocker of amino groups to temporarily mask them from reactivity while another... 

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