A specific role of 43Ca in the enzymatic ATP synthesis

Abstract

This is the first report ever on the nuclear spin selective 43 Ca 40 Ca isotope effect expressed in the Calcium affected enzymatic ATP synthesis. Once the creatine kinase (CK) catalytic sites were loaded with 43 Ca 2+ , the resulting enzyme activity goes up (2.0±0.3 – fold) compared to the CKdirected ATP synthesis rate occurred in the presence of nonmagnetic, spinless, 40 Ca nuclei. The effect manifests itself predominantly within a high concentration range (Calcium chloride,40 mM) indicating that the ATP synthesis is a spin-selective ion-radical process. Primary reaction of this path is an electron transfer between the reaction partners, С a(H2O)n 2+ ( n ≤ 4) and Ca(ADP) 3- , generating an ion-radical pair where the singlet -triplet spin conversion takes place as a result of the nuclear spin selectivity and a consequent magnetic isotope effect. This, in turn, makes an essential impact on the final reaction’s ATP yield. To the contrast, there is no any isotope effect found within a low Ca 2+ concentration range showing that the ATP synthesis proceeds in a most common nucleophylic way. The submolecular mechanisms of phenomena described and their possible applied significance are under discussion.