Succinylation of glyceraldehyde-3-phosphate dehydrogenase from Bacillus stearothermophilus. A reactive threonine residue in the apoenzyme.

1. Glyceraldehyde-3-phosphate dehydrogenase from bacillus stearothermophilus can be extensively succinylated in the presence of substrates and coenzyme without appreciable loss of activity. 2. The apoenzyme in the absence of substrates is rapidly inhibited by small amounts of succinic anhydride. NAD+, glyceraldehyde-3-phosphate and inorganic phosphate all afford protection from inhibition, and inhibition is slowly reversed in the presence of pyrophosphate at pH 8.5. 3. Kinetic and spectral studies have shown that the specific inhibition is associated with the succinylation of the aliphatic hydroxyl group of a serine or threonine residue. 4. The residue specifically succinylated has been identified as one of the two threonine residues, most probably Thr-150, adjacent to the activ-site cysteine residue in the primary structure. Its unusual reactivity is discussed in relation to the three-dimensional structure of the enzyme. 5. A second residue, a lysine homologous with Lys-212 in the pig muscle enzyme, can be succinylated in both holoenzyme and apoenzyme with no detectable effect upon the enzymic activity.