Location of exposed and buried cysteine residues in the polypeptide chain of aspartate aminotransferase

Identification of the reactive sulphydryl group of mitochondrial aspartate aminotransferase from pig heart

“…Although the reagent used was different from that employed by Gehring and Christen [11 ] there seems to be no reason to suppose that the site of reaction will be different in the two cases. In support of this view, the order of reactivities of the cysteine residues of s-AAT is the same with a variety of reagents [1 ] including iodoacetic acid [3,5,6].…”

“…The cysteine residues of cytoplasmic aspartate aminotransferase (s-AAT) from pig heart have been extensively investigated [1][2][3][4][5][6]. In the native protein, the five sulphydryl groups per polypeptide chain fall into three classes on the basis of their reactivities.…”

A rapid preparation of the apo—holo hybrid of aspartate aminotransferase

“…The 3 classes of reactive sulfhydryl groups can be identified as Cys45, Cys-82 and Cys-390, respectively [20,21]. Cys-45 and Cys-82 are exposed and readily reactive, whereas Cys-390 is semi-buried, susceptible to syncatalytic modification and located near the active site [22].…”

Modification of aspartate aminotransferase with heavy atoms and with coenzyme analogs

“…Reaction of cysteine-45 with other sulfhydryl reagents has no effect on the activity (Zufarova ejt , 1973;Wilson et al, 1974). Cysteine-45 can be selectively modified by NEM, DTNB, TNM • (Wilson et^ a^., 1974), or maleate (Polyanovsky et^ a^., 1973a).…”

“…Its location in such a rigid structure explains why this residue was not accessible to most sulfhydryl reagents except in the denatured protein (Wilson et aj_., 1974;Polyanovsky et , 1973a;Zufarova e_t , 1973). The small size of methylmercury and the nonpolar nature of its methyl group must enable this reagent to penetrate into the hydrophobic core of the protein.…”