Investigation of the preferred Mg(II)-adenine-nucleotide complex at the active site of ectonucleotidases in intact vascular cells using phosphorothioate analogues of ADP and ATP.

In the presence of Mg2+ the ecto-(nucleoside diphosphatase) on intact vascular endothelial or smooth muscle cells in culture selectively catabolizes the PS diastereoisomer of adenosine 5'-[alpha-thio]diphosphate, (PS)-ADP [alpha S], and the ecto-(nucleoside triphosphatase) selectively catabolizes the PS isomer of adenosine 5'-[beta-thio]triphosphate, (PR)-ATP[beta S], but exhibits no selectivity towards ATP[alpha S] isomers. In the presence of Cd2+ selectivity to ADP[alpha S] and to ATP[beta S] isomers is reversed; in the presence of Co2+, selectivity is lost. We conclude that each enzyme preferentially recognises the lambda (screw-sense) bidentate Mg(II)-nucleotide complex at its active site.