(Rp)‐ and (Sp)‐8‐piperidino‐adenosine 3′,5′‐(cyclic)thiophosphates discriminate completely between site A and B of the regulatory subunits of cAMP‐dependent protein kinase type I and II

Abstract
8‐Piperidino‐cAMP has been shown to bind with high affinity to site A of the regulatory subunit of cAMP‐dependent protein kinase type I (AI) whereas it is partially excluded from the homologous site (AII) of isozyme II [Øgreid, D., Ekanger, R., Suva, R. H., Miller, J. P., and Døskeland, S. O. (1989), Eur. J. Biochem. 181, 19–31]. To further increase this selectivity, the (RP)‐ and (SP)‐diastereoisomers of 8‐piperidino‐cAMP[S] were synthesized and analyzed for their potency to inhibit binding of [3H]cAMP to site A and site B from type I (rabbit skeletal muscle) and type II (bovine myocardium) cAMP‐dependent protein kinases.(SP)‐8‐Piperidino‐cAMP[S] showed an enhanced relative affinity for site AI, thus being by far the best A‐selective compound (more than 100‐fold) tested for this isozyme. In contrast, the (RP)‐ isomer was less selective for AI than 8‐Piperidino‐cAMP itself. The reduction in affinities for BII, compared to 8‐piperidino‐cAMP, were 10‐fold and 50‐fold for the (SP)‐ and (RP)‐isomer, respectively. Both isomers were almost completely excluded from AII, with affinities about 1000‐fold lower than 8‐piperidino‐cAMP itself. The (RP)‐isomer selected BII with an affinity about 10000 times higher than for AII, whereas the (SP)‐isomer showed a preference of about 70000‐fold in favour of BII. 8‐Piperidino‐cAMP as well as its (SP)‐isomer activated both types of holoenzyme protein kinases whereas the (RP)‐isomer acted as an antagonist of cAMP‐induced activation.The study concludes that the combination of piperidino‐ and exocyclic sulfur substitutions generate cAMP analogs that completely discriminate between site A and B of cAMP‐dependent protein kinases.

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