Affinity Labelling to ‐ SH Groups in Adenosine ‐ Triphosphate ‐ Phosphoribosyl Transferase with the Dinitrophenyl Group from S‐Dinitrophenyl‐6‐mercaptopurine‐riboside 5′‐Phosphate

Adenosine–triphosphate–phosphoribosyl transferase from Escherichia coli reacts with S-dinitrophenyl-6-mercaptopurine-riboside 5′-phosphate. In this reaction the dinitrophenyl group becomes attached to the enzyme, while the nucleotide is split off. Most aliphatic high and low-molecular-weight –SH compounds react with the thioether in the opposite way, i.e. bind the nucleotide and split off dinitrothiophenol. It appears that the dinitrophenyl moiety of the thioether interacts with the enzyme in a specific way, and that this interaction activates the bond between the dinitrophenyl group and the sulfur atom. In support of this it was found that dinitrophenol inhibits the transferase reaction with half maximal effect at 0.4 mM. The inhibition is competitive with ATP. Dinitrophenol also competes with ATP in binding studies.