Allosteric activation of rat liver microsomal [hydroxymethylglutaryl-CoA reductase (NADPH)]kinase by nucleoside phosphates.
Microsomal 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase kinase activity is enhanced about 5 fold by 2 mM of either AMP or ADP. Activation constants, Ka, for AMP and ADP are 17 microM and 430 microM respectively, showing that AMP is a more potent activator than ADP. This property is expressed by increasing not only the rate of reductase inactivation but also the rate of reductase phosphorylation from [gamma-32P]ATP. GTP can replace ATP as substrate of reductase kinase but GMP and GDP cannot replace AMP as activators. Kinetic studies show that ATP can only act as a substrate. Nucleoside mono or diphosphates and nucleoside triphosphates, thus, appear to bind to different sites on microsomal HMG-CoA reductase kinase. Nucleoside mono or diphosphates act as allosteric activators of reductase kinase. The adenosyl moiety and the unaltered phosphate ester at the 5' position are two essential features of the activator molecule. Phosphorylation of reductase either by microsomal or cytosolic AMP-activated reductase kinase produces an 80% inactivation, with a concomitant incorporation of 0.8 mol of 32P per mol of reductase (Mr 55,000). In both cases exhaustive tryptic digestion of 32P-labeled HMG-CoA reductase, which had been denatured in 2M urea, yields two major phosphopeptides, the phosphoryl group being bound to serine residues.
A
A
Ferrer
C
C
Caelles
N
N
Massot
F G
FG
Hegardt
D055372:AMP-Activated Protein Kinases; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000249:Adenosine Monophosphate / Q000494:pharmacology; D000494:Allosteric Regulation; D000818:Animals; D055598:Chemical Phenomena; D002621:Chemistry; D004789:Enzyme Activation / Q000187:drug effects; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism; D008862:Microsomes, Liver / Q000201:enzymology*; D009097:Multienzyme Complexes / Q000378:metabolism*; D009711:Nucleotides / Q000494:pharmacology*; D010446:Peptide Fragments / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D051381:Rats; D014357:Trypsin / Q000378:metabolism
D009097:Multienzyme Complexes; D009711:Nucleotides; D010446:Peptide Fragments; D010768:Phosphoserine; D000249:Adenosine Monophosphate; D000244:Adenosine Diphosphate; D006903:Hydroxymethylglutaryl CoA Reductases; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D014357:Trypsin