Complexes of serine acetyltransferase and isozymes of cysteine synthase in spinach leaves.

Polyclonal antibodies against cysteine synthase (CSase; EC 4.2.99.8) isozymes 1, 2, and 3 were used for the detection of complexes of these isozymes with serine acetyltransferase (SATase; EC 2.3.1.30). SATase was partially purified and found to complex with these isozymes by western blotting and immunotitration. When the complexes were treated with a high concentration of O-acetyl-L-serine, they did not dissociate. However, some complexes with CSase 1 or 3 dissociated when left for 24 h at 4 degrees C. Results of western blotting on SDS-PAGE showed that CSase 2 complexed with SATase. CSases 1, 2, and 3 all could complex with SATase, but the tightness of the bond differed.