Open AccessThe Reactive Sulfhydryl Groups of Cytoplasmic Aspartate Aminotransferase
Author(s) -
Wilson Kenneth J.,
Birchmeier Walter,
Christen Philipp
Publication year - 1974
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1974.tb03289.x
Subject(s) - tetranitromethane , chemistry , thiol , enzyme , reactivity (psychology) , protein subunit , cysteine , stereochemistry , cytoplasm , biochemistry , medicine , alternative medicine , pathology , gene
The two readily reacting sulfhydryl groups out of a total of five per subunit of cytoplasmic aspartate aminotransferase have been identified as those in positions 45 and 82 of the primary structure. Cys 45 exhibits approximately a 20‐fold higher reactivity toward 5,5′‐dithiobis‐(2‐nitrobenzoate) and tetranitromethane than Cys 22 . The alterations in enzymatic activity observed following blockage of these two thiol groups by N ‐ethylmaleimide and tetranitromethane, 125% and 60% of the initial enzymatic activity, respectively [Birchmeier, W., Wilson, K. J. & Christen, P. (1973) J. Biol. Chem. 248 , 1751] are due to the modification of the faster‐reacting Cys 45 . The rate of modification at both thiol groups is independent of the presence of the substrates. The fluorescence properties of N ‐dansylcysteine substituents at both Cys 45 and Cys 82 indicate a polar environment corresponding to their localization on the exterior of the enzyme molecule.