Lysine as the substrate binding site of porphobilinogen synthase of Rhodopseudomonas spheroides.

The 14C labelled inactive protein obtained by sodium borohydride reduction of the enzyme, porphobilinogen synthase of Rhodopseudomonas spheroides, in the presence of [4-14C]5-aminolevulinic acid, gave on acid hydrolysis and subsequent electrophoresis or two-dimensional chromatography a major radioactive spot which was confirmed to be N-epsilon-[4-(-5aminovaleric acid)]lysine (ALA-lysine) by comparing its co-chromatographic and electrophoretic behaviour with the chemically synthesized ALA-lysine. An epsilon-NH2 group of lysine residue of porphobilinogen synthase, is thus the binding site of the substrate, 5-aminolevulinic acid.