The Binding of Specific Ligands to Adenosine‐Triphosphate Phosphoribosyltransferase

Publisher Website
Google Scholar
Abstract
Ligand binding by ATP phosphoribosyltransferase was studied by different methods. Enzyme [200,000 daltons] bound approximately 3 molecules of histidine cooperatively with a Hill plot slope of 1.23 (half-maximal binding at 520 .mu.M). AMP increased the affinity of the enzyme for histidine (half-maximal binding at 80 .mu.M). In the presence of AMP the binding of histidine was strongly cooperative with a Hill plot slope of 2.3. The transferase binds a litle more than 3 molecules of AMP/hexamer of enzyme with a dissociation constant of the transferase .cntdot. AMP complex of approximately 25 .mu.M. ATP was able to displace radioactive AMP from the enzyme only at a concentration ratio of 25 in favor of ATP. The transferase bound 3 molecules of ATP/200,000 daltons to an inhomogeneous population of sites, or by a mechanism of negative cooperativity. The binding of phosphoribosyl ATP took place preferably at 1-2 sites/hexamer of enzyme, depending on several factors including the Mg concentration.

This publication has 17 references indexed in Scilit: