Affinity labeling of succinyl-CoA synthetase from Escherichia coli by the 2',3'-dialdehyde derivative of adenosine 5'-diphosphate

Chemical modification of tryptophan residues in Escherichia coli succinyl-CoA synthetase. Effect on structure and enzyme activity

Succinyl-CoA synthetase of Escherichia coli is an alpha 2 beta 2 protein containing active sites at the interfaces between alpha- and beta-subunits. The alpha-subunit contains a histidine residue that is phosphorylated during the reaction. The beta-subunit binds coenzyme A and probably succinate [see Nishimura, J. S. (1986) Adv. Enzymol. Relat. Areas Mol. Biol. 58, 141-172]. Chemical modification studies have been conducted in order to more clearly define functions of each subunit. Tryptophan residues of the enzyme were modified by treatment with N-bromosuccinimide at pH 7. There was a linear relationship between loss of enzyme activity and tryptophan modified. At one tryptophan residue modified per beta-subunit, 100% of the enzyme activity was lost. In this enzyme sample, one methionine residue in each alpha- and beta-subunit was oxidized to methionine sulfoxide, although loss of enzyme activity could not be related in a linear manner to the formation of this residue. Subunits were prepared from enzyme that was inactivated 50% by N-bromosuccinimide with 0.5 tryptophan modified per beta-subunit but with insignificant modification of methionine residues in either subunit. Small decreases in the tyrosine and histidine content were observed in the alpha-subunit but not in the beta-subunit. In this case, modified beta-subunit when mixed with unmodified alpha-subunit gave a population of molecules that was 50% as active as the refolded, unmodified control but was only slightly changed with respect to phosphorylation capacity and unchanged with respect to rate of phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)

Affinity labeling of the (Na+ + Mg2+)-ATPase from Acholeplasma laidlawii B membranes by the 2',3'-dialdehyde derivative of adenosine 5'-triphosphate

The (Na+ + Mg2+)-ATPase of the Acholeplasma laidlawii B plasma membrane was inactivated by the 2',3'-dialdehyde derivative of ATP (oATP). oATP behaved as a reversible competitive inhibitor of this ATPase and was slowly hydrolyzed by the enzyme. In addition, oATP induced an irreversible inactivation of the enzyme. A 62% inactivation of the enzyme correlated with the binding of 16 moles of oATP per mole of the enzyme. In the presence of 5'-adenylyl imidodiphosphate, a non-hydrolyzable substrate analogue, the stoichiometry was 8 moles oATP per mole of ATPase. By SDS-polyacrylamide gel electrophoresis, [U-14C]oATP was found to bind covalently to four of the five subunits of the enzyme, but specific labeling was highest for the gamma-subunit of the ATPase.