Stimulation of rat liver AMP-activated protein kinase by AMP analogues

Stimulation of AMP-activated protein kinase (AMP-PK) by ZMP (5-amino-4-imidazolecarboxamide ribotide, AICAR), formed by adenosine kinase upon addition of AICA riboside to isolated rat hepatocytes, results in inhibition of fatty acid and cholesterol synthesis by inactivation of acetyl-CoA carboxylase and 3-hydroxy-3-methylglutaryl-CoA reductase, respectively (Henin et al. (1995) FASEB J. 9, 541-546). The effects of ZMP and other AMP analogues have now been compared with those of AMP on AMP-PK purified from rat liver. ZMP stimulated AMP-PK to the same maximal extent as AMP (about 10-fold). ZMP had less affinity for AMP-PK than AMP, but this affinity was similarly influenced by ATP: half-maximal effects, requiring 0.4 mM AMP or 5 mM ZMP at 3 mM ATP, were obtained with 9 mu M AMP or 0.4 mM ZMP at 0.2 mM ATP. The kinetic parameters of AMP-PK for the SAMS peptide and for ATP were influenced in the same way by ZMP and AMP. Stimulation of AMP-PK by ZMP was additive with AMP, up to when maximal stimulation was obtained. Taken together, these results indicate that ZMP binds to the same site as AMP on AMP-PK. Tubercidin 5'-monophosphate, 2'-deoxy-AMP and Ara-AMP stimulated AMP-PK, but N-6-methyl-AMP, 1,N-6-etheno-AMP, 6-mercaptopurine riboside 5'-monophosphate, adenylosuccinate and succinyl-AICAR were ineffective, suggesting that a free 6-NH2 group may be important for binding of effecters to AMP-PK.