Correlation between enzyme activity and hinge‐bending domain displacement in 3‐phosphoglycerate kinase

Diffuse X‐ray‐scattering data give evidence for large‐scale structural change in pig muscle 3‐phosphoglycerate kinase upon substrate binding. Simultaneous binding of 3‐phosphoglycerate and MgATP either to the unmodified enzyme or to its active methylated derivative leads to about an 0.1‐nm decrease in radius of gyration. These data coincide well with the previous data for yeast 3‐phosphoglycerate kinase. When, instead of methylation, the two reactive thiol groups of pig muscle 3‐phosphoglycerate kinase are carboxamidomethylated, the enzyme becomes inactive and the radii of gyration of its ‘apo’ and ‘holo’ forms do not differ within limits of experimental error. Thus, a correlation exists between the activity of 3‐phosphoglycerate kinase and its substrate‐induced largescale conformational change. This correlation is a strong argument in favor of the functional importance of domain locking in the reaction catalyzed by 3‐phosphoglycerate kinase.