Cyclic adenosine 3':5' monophosphate dependent protein kinase. Interaction with butyrylated analogues of cyclic adenosine 3':5' monophosphate
The authors chromatographically purified butyrylated analogues of cyclic adenosine 3':5' monophosphate (cAMP) to displace [3H]cAMP bound to a partially purified bovine muscle protein kinase preparation. O2' Monobutyryl cAMP (O2MBC) showed a linear displacement of label, with an affinity equal to 1.5% that of cAMP. N6 Monobutyryl cAMP (N6MBC) and N6,O2' dibutyryl cAMP (DBC) show curvilinear displacement consistent with at least two types of binding sites. The most abundant of these sites does not appear to discriminate N6 butyrylated cAMPs from the N6 unsubstituted compounds. The less abundant site (20% of total) does distinguish N6 butyryl substituted compounds (e.g. N6MBC has 100% the affinity of cAMP for the most abundant site and 7% for the less abundant site). The ability of these purified analogues to stimulate the kinase activity (assayed as 32P incorporation into casein) of our preparation showed a similar rank order as the binding studies. Initial rates of the enzyme reaction (relative to cAMP = I.O) were: 0.29 for N6MBC, 0.002 for O2MBC, and 0.0003 for DBC. It is concluded from these studies that: DBC is unlikely to mimic cAMP action through direct intracellular interaction with cAMP dependent protein kinase; N6MBC is probably the active butyrylated analogue of cAMP; while N6MBC binds well to some sites it binds less effectively to others and this observation may account for observations regarding divergent biological effects of cAMP and its butyrylated analogues.