[Study of yeast phosphoglycerate kinase by electron paramagnetic resonance. 1. Modification of protein SH-group by spin labels. Conformational changes of enzyme].

The conditions for modifications of a single SH-group of phosphoglycerate kinase from yeast by maleimid spin label and the mercury-containing spin labels were defined. The time course of immobilization of mercury containing paramagnetic radicals was obtained. Based on changes in EPR spectra we calculated dissociation constants for complexes of phosphoglycerate kinase with 3-phosphoglycerate and sulfate ions. Distinct substances were shown to induce different changes in enzyme conformation. It was concluded that approach of enzyme domains is caused by the binding of 3-phosphoglycerate-a specific substrate of this enzyme.