Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K31/00—Medicinal preparations containing organic active ingredients
  • A61K31/70—Carbohydrates; Sugars; Derivatives thereof
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K31/00—Medicinal preparations containing organic active ingredients
  • A61K31/33—Heterocyclic compounds
  • A61K31/395—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins
  • A61K31/41—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins having five-membered rings with two or more ring hetero atoms, at least one of which being nitrogen, e.g. tetrazole
  • A61K31/415—1,2-Diazoles
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K31/00—Medicinal preparations containing organic active ingredients
  • A61K31/33—Heterocyclic compounds
  • A61K31/395—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins
  • A61K31/495—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins having six-membered rings with two or more nitrogen atoms as the only ring heteroatoms, e.g. piperazine or tetrazines
  • A61K31/505—Pyrimidines; Hydrogenated pyrimidines, e.g. trimethoprim
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K31/00—Medicinal preparations containing organic active ingredients
  • A61K31/33—Heterocyclic compounds
  • A61K31/395—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins
  • A61K31/495—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins having six-membered rings with two or more nitrogen atoms as the only ring heteroatoms, e.g. piperazine or tetrazines
  • A61K31/505—Pyrimidines; Hydrogenated pyrimidines, e.g. trimethoprim
  • A61K31/519—Pyrimidines; Hydrogenated pyrimidines, e.g. trimethoprim ortho- or peri-condensed with heterocyclic rings
  • A61K31/52—Purines, e.g. adenine
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P3/00—Drugs for disorders of the metabolism
  • A61P3/06—Antihyperlipidemics

Definitions

• This invention relates to methods for treating animals having elevated serum lipid levels, e.g. , animals suffering fromhypertriglyceridemia , hypercholesterolemia , atherosclerosis or obesity.
• Mild hypertriglyceridemia without much elevation of cholesterol (e.g. , Type IV hyperlipoproteinemia of Fredrickson) , is quite common in several disorders, including uncontrolled diabetes mellitus, renal failure, systemic lupus erythematosus, alcoholism, obesity (Schaeffer & Levy, 312 New England J. Medicine 1300, 1985), and as recently reported, AIDS (Grunfeld et al., 90 Am J. Med. 154, 1991). Mild hypertriglyceridemia can be aggravated by stress and various medications, such as estrogens, oral contraceptives, beta-blockers and thiazides.
• various medications such as estrogens, oral contraceptives, beta-blockers and thiazides.
• Mild hypertriglyceridemia is generally due to an increase in very low density lipoproteins (VLDLs) , caused by an increase in lipid synthesis, as well as a decrease in catabolism.
• VLDLs very low density lipoproteins
• the association of mild hypertriglyceridemia with atherosclerosis is less well established than that of hypercholesterolemia with atherosclerosis (Schwandt, 11 Eur. Heart J. Suppl. H 38, 1990) .
• One reason for this may be the very high intraindividual variability of fasting triglyceride levels (Brenner & Heiss, 11 Eur. Heart J. 1054, 1990).
• Mild hypertriglyceridemia should be treated, particularly in diabetics (Lewis et al., 72 J. Clin. Endocrinol. Metab. 934, 1991).
• bile-acid sequestrants e.g. , cholestyramine, colestipol
• One of their side-effects is an increase in triglycerides.
• Stimulators of lipoprotein lipase act by increasing the activity of lipoprotein lipase, and thereby decrease the plasma VLDL and triglyceride levels. They are useful in treatment of hypertriglyceridemia, although not all patients respond. In addition, they may induce an increase in total cholesterol, and in LDL cholesterol.
• Inhibitors of triglyceride and VLDL synthesis act by decreasing lipolysis in adipose tissue, and consequently the supply of fatty acids available for esterification into triglycerides in the liver.
• Niacin nicotinic acid
• a major problem with niacin is intense flushing and pruritus due to prostaglandin release. It also has an hyperglycemic effect which renders insulin adjustment in diabetics necessary.
• Gemfibrozil (a derivative of pentenoic acid) stimulates lipoprotein lipase and the synthesis of HDL.
• HMG-CoA reductase e.g.. mevastatin, lovastatin
• HMG-CoA reductase rate-limiting enzyme
• HMG-CoA reductase inhibitors can produce muscle abnormalities in humans and corneal opacities in experimental animals, but have not been found to produce serious side-effects (Grundy, 319 New England J. Medicine 24, 1988).
• This invention relates to a novel means for decreasing the level of triglycerides, cholesterol and other related lipids in human or other animal plasma.
• the method is based upon the finding that AICAriboside onophosphate (ZMP) , and related analogs (which are structural mimetics of AMP) , are effective in reducing the amount of synthesis of these lipids.
• ZMP AICAriboside onophosphate
• AMP- activated protein kinase which regulates the activity of enzymes that control the synthesis of fatty acids, cholesterol, and a lipase which may in turn effect the action of lipolytic hormones.
• the compounds may block the action of lipolytic hormones on adipose tissue hormone-sensitive lipase, and thereby prevent release of fatty acids for export to liver for re- esterification into triglycerides.
• administration of these compounds to an animal having elevated serum lipid levels is effective to lower such lipid levels, and thus is a treatment for hypertriglyceridemia, hypercholesterolemia and obesity.
• the invention features a method for treating an animal, e.g.. one having an elevated serum lipid level.
• the method may include the step of identifying an animal having such an elevated serum lipid level.
• the method includes introducing into that animal a lipid-lowering amount of an AMP mimetic, or pro-drug (a compound which can be administered (e.g., orally) to generate an AMP mimetic in vivo. e.g.. it includes compounds which upon administration are activated to produce the AMP mimetic, e.g..
• elevated is meant to encompass a level of lipid which is above an accepted normal range for that lipid in the animal, or which is known to be associated with a pathologic process. Such levels can be measured by any standard means, for example, they can be measured chemically, biochemically, or even by study of the symptoms of an animal which may reflect an elevated lipid level. Such symptoms may include disorders which are commonly associated with elevated lipid levels, such as diabetes mellitus, renal failure, atherosclerosis, heart disease, stroke, etc.. as discussed above. Thus, to the extent that an animal may not be specifically diagnosed as having an elevated lipid level, it is appropriate in this invention to treat animals which have a significant potential of having such elevated lipid levels.
• the term "identif ing” includes identifying those animals which have such a significant potential.
• the phrase "significant potential” includes those disorders which are commonly recognized by those skilled in the art as being associated with elevated lipid levels. For example, it can be concluded that an elevated serum lipid level is present in obese persons (i.e.. those having excess adipose tissue) or those with the effects of elevated lipids (e.g.. those having atherosclerosis or atherosclerosis-related complications, such as transient ische ic attacks, strokes, heart attacks, angina, and peripheral vascular diseases) .
• lipid is meant to include any of a large number of lipids present in the serum of an animal, including (as discussed above) but not limited to cholesterol, triglycerides, lipoproteins, low density lipoproteins, very low density lipoproteins, and chylomicrons.
• the method for treating includes introducing the desired AMP mimetic or pro-drug by any standard methodology, including transdermal, injection into muscle tissue, or blood stream, or by oral or other parenteral administration.
• a “lipid-lowering amount” includes an amount which is effective over a period of several hours or days to lower the serum lipid level in a way which can be detected either chemically, biochemically, or by a change in the appearance or symptoms of the patient. That is, "lipid lowering” means a lowering of the level of lipid in a clinically significant manner, well known to those of ordinary skill in the art.
• AMP mimetics or pro-drugs are well known to those in the art and include, e.g.. AICAriboside (5'-amino-4- imidazolecarboxamide riboside) , AICAribotide (ZMP) , and analogs thereof, and any pro-drugs which can be used to produce such AICAriboside, ZMP, and analogs thereof, within an animal body, or tubercidin (4-amino-l- ⁇ -D- ribofuranosylpyrrolo[2,3-d]pyrimidine) , tubercidin base, tubercidin monophosphate, and prodrugs thereof, which can produce AMP mimetics within a body of the animal being treated.
• AICAriboside 5'-amino-4- imidazolecarboxamide riboside
• ZMP AICAribotide
• any pro-drugs which can be used to produce such AICAriboside, ZMP, and analogs thereof, within an animal body
• tubercidin
• pro-drugs and related analogs described in PCT Application WO 90/09163, published August 23, 1990 are potentially useful in this invention.
• Such mimetics can be synthesized by the methods described in this publication.
• base is meant a compound which when phosphoribosylated is a nucleotide and serves as an AMP mimetic.
• AMP-mimetics or pro-drugs which are suitable for lipid-lowering within an animal can be readily identified by any standard biochemical test, e.g.. drug pharmacokinetics, measurement of lipid levels in biological fluids, or lipid metabolism, either in vivo or in vitro. Examples of such tests are described below.
• AMP mimetics or pro-drugs are used in such tests, and those useful in this invention provide results similar to or better than AICAriboside.
• Other examples of such tests are provided by Davies et al., 186 Eur. J. Biochem. 123, 1989 and Carling et al., 186 Eur. J. Biochem. 129, 1989.
• the pro-drugs and related drugs such as those described in PCT 90/09163, can be readily screened to determine whether they are useful in the method of this invention.
• AMP-activated protein kinases are well known to those in the art. For example, one embodiment is described in numerous publications by Dr. Hardie and his colleagues, see. Hardie et al., 14 Trends Biochem. Sci. 20, 1989; Munday et al., 175 Eur. J. Biochem. 31, 1988; Davies et al., 187 Eur. J. Biochem. 183, 1990; Sim and Hardie, 233 FEBS LETTERS 294, 1988; Munday et al., 235 FEBS LETTERS 144, 1988; Carling et al., 186 Eur. J. Biochem. 129, 1989; and Davies et al., 186 Eur. J. Biochem. 123, 1989.
• This invention provides a simple way in which several lipid synthesis pathways can be simultaneously inhibited. This inhibition can be produced by administration of a single drug, as discussed above, and thus has significant advantages over prior art methods of lowering lipid synthesis which require administration of several drugs. In addition, the inhibition by a drug of this invention also causes inhibition of hepatic synthesis of triglycerides, which had not to date been possible.
• the method of this invention is advantageous since it specifically inhibits activity of liver-specific proteins, and has little or no effects in certain other tissues, such as cornea and muscle tissues.
• the drugs are also advantageous since they control both lipid and cholesterol biosynthesis, and are potentially far more potent than existing drugs.
• Fig. 1 is a schematic representation of two lipid synthesis pathways in animals
• Fig. 2 is a graph showing the effect of AICAriboside on synthesis of fatty acids from endogenous substrates
• Fig. 3 is a graph showing the dose effect of AICAriboside on synthesis of fatty acids from glucose
• Fig. 4 is a graph showing the dose effect on AICAriboside on synthesis of fatty acids from lactate;
• Fig. 5 is a graph showing the effect of AICAriboside on synthesis of fatty acids from leucine;
• Fig. 6 is a graph showing the effect of AICAriboside on synthesis of fatty acids from 2-ketoisocaproate
• Fig. 7 is a graph showing the effect of AICAriboside on acetyl-CoA carboxylase activity in isolated hepatocytes
• Fig. 8 is a graph showing the effect of AICAriboside on incorporation of tritiated water into lipids.
• Fig. 9 is a graph showing the effect of AICAriboside on the non-saponifiable lipid fraction.
• Fig. 10 is a graph showing the effect of IP injection of AICAriboside (500 g/kg) on rat liver HMG-CoA reductase activity.
• Figs. 11 and 12 are graphs showing AMP-stimulated protein kinase activity relative to ZMP and AMP concentrations.
• Fig. 13 is a histogram showing AMP-stimulated protein kinase activity by AMP and other reagents.
• Fig. 1 the following is a brief description of the various biochemical pathways, and enzymes involved therein, which are related to the utility of this invention.
• triglycerides are synthesized mainly in the liver, from fatty acids either newly synthesized by the liver itself, or coming from lipolysis in adipose tissue.
• Hepatic synthesis of fatty acids includes the conversion of various substrates into acetyl-CoA, e.g.. glucose and other monosaccharides, such as fructose and galactose, lactate, pyruvate, ketogenic amino acids and their keto derivatives.
• Acetyl-CoA is converted into malonyl-CoA by acetyl-CoA carboxylase.
• Malonyl-CoA is subsequently elongated into long-chain fatty acyl-CoA, which is esterified into triglycerides with glycerol 3-phosphate. These triglycerides are exported toward peripheral tissues, including adipose tissue, in the form of very-low-density lipoproteins. Lipoprotein lipase, located at the outer surface of peripheral cells, hydrolyzes the triglycerides to fatty acids and glycerol which can be taken up by the cells.
• Acetyl-CoA carboxylase is the rate-limiting enzyme of hepatic fatty acid synthesis. Its activity is controlled by citrate, which is stimulatory, and by long-chain fatty acyl-CoA, which is inhibitory. Acetyl-CoA carboxylase is moreover regulated by reversible phosphorylation/ dephosphorylation. The dephosphorylated form of acetyl- CoA carboxylase is active, and the phosphorylated form inactive.
• a variety of protein kinases including cAMP- dependent protein kinase and protein kinase C, are able to phosphorylate acetyl-CoA carboxylase in vitro.
• acetyl-CoA is first converted into acetoacetyl-CoA, and thereafter into 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) .
• HMG-CoA reductase is the rate limiting step of cholesterol synthesis.
• An ensuing 9 step sequence leads from mevalonate to cholesterol.
• HMG-CoA reductase is located inside the smooth endoplasmic reticulum. Expression of the enzyme is regulated by the cholesterol level: excess cholesterol decreases the synthesis of the protein and increases its degradation.
• HMG-CoA reductase is regulated by phosphorylation/dephosphorylation.
• Purified HMG-CoA reductase can be phosphorylated and inactivated in vitro by several protein kinases, including protein kinase C, a Ca ⁇ /calmodulin-dependent protein kinase, and AMP-activated protein kinase (Hardie et al., 14 Trends Biochem. Sci. 20, 1989) .
• AMP- activated protein kinase phosphorylates HMG-CoA reductase in vivo (Clarke & Hardie, 9 EMBO Journal 2439, 1990).
• AMP-activated protein kinase belongs to a group of enzymes which, using ATP, phosphorylate proteins at serine or occasionally threonine residues. Best known in this group are cyclic AMP-dependent protein kinase (cA-
• Protein kinases are components of the transduction mechanisms whereby hormones and other factors regulate physiological functions. Their action elicits conformational changes that modify either the catalytic activity of enzymes or the function of other regulatory proteins. The conformational changes induced by phosphorylation can be reversed by protein phosphatases, of which several types have been characterized in recent years.
• AMP-PK phosphorylates three enzymes, each catalyzing a key regulatory step of lipid metabolism: [1] acetyl-CoA carboxylase, the rate-limiting step of fatty acids synthesis, which is most active in liver; [2] HMG-CoA reductase, the first committed step of cholesterol synthesis, also predominantly located in liver; and [3] hormone-sensitive lipase, the enzyme that controls the release of fatty acids from triglycerides in adipose tissue (Hardie et al., 14 Trends Biochem. Sci 20, 1989).
• AMP-PK In accordance with its role in lipid metabolism, the highest activities of AMP-PK are found in liver and lactating mammary gland, which are very active in both fatty acid and cholesterol synthesis (Davies et al. , 186 Eur. J. Biochem. 123, 1989). Lower activities exist in tissues which have an active fatty acid metabolism, namely, adipose tissue, adrenal cortex, lung, macrophages and heart. The tissues with the lowest activity of AMP-PK are brain and muscle, two tissues in which rates of lipid synthesis are very low, at least in adults.
• AMP-PK has been purified 4800-fold from rat liver, to a specific activity of 1.25 ⁇ mol/min/mg (Carling et al., 186 Eur. J. Biochem. 129, 1989) . Although the preparation did not display a single band on an electrophoretic gel, the fact that its specific activity was comparable with that of other protein kinases suggests that it was approaching homogeneity. Molecular mass of subunits is estimated at 63 kDa, and of the holoenzyme at 100 + 30 kDa, indicating that native AMP-PK might be a dimer. Mos investigations of the catalytic properties of AMP-PK have been performed with acetyl-CoA carboxylase as substrate.
• AMP-PK In the absence of AMP, AMP-PK has a Km of 86 ⁇ M for ATP and of 1.9 ⁇ M for acetyl-CoA carboxylase. AMP increases Vmax 3- to 6-fold, without significantly modifying Km for either ATP or acetyl-CoA carboxylase.
• the sensitivity to AMP depends on the concentration of ATP: at 0.2 mM ATP, half-maximal stimulation by AMP is observed at 1.4 ⁇ M; at the near-physiological ATP concentration of 2 mM, half-maximal stimulation requires 14 ⁇ M AMP.
• Some AMP analogues are reported ineffective as substituting for AMP (Carling et al., 186 Eur. J. Biochem. 129, 1989).
• 8-bromoadenosine 5-monophosphate is a weak stimulator at low concentrations, but it is an inhibitor at high concentrations.
• the regulatory concentrations of AMP are an order of magnitude lower than those measured in acid extracts of liver. However, the latter have often been claimed to be artefactual, resulting from degradation of ATP. Calculations based on equilibrium constants and nuclear magnetic resonance studies have led to estimates that the free concentration of liver AMP may be around 1 ⁇ M. Any increase in AMP within this range would thus potently stimulate AMP-PK.
• AMP-PK has been shown to inactivate acetyl-CoA carboxylase in a cell-free system by phosphorylating Ser- 79 of the protein (Hardie et al., 14 Trends Biochem. Sci 20, 1989). Addition of glucagon to intact cells, namely isolated rat hepatocytes and adipocytes, also results in the phosphorylation of Ser-79. In a cell-free system, however, cA-PK, which as a rule mediates the actions of hormones that elevate cyclic AMP, phosphorylates a different serine, namely Ser-77.
• AMP-PK inactivates HMG-CoA reductase by phosphorylating Ser-872 of the enzyme (Clarke & Hardie, 9 EMBO Journal 2439, 1990). This phosphorylation is most likely responsible for the inactivation of HMG-CoA reductase known to occur when special precautions (e.g.. freeze-clamping) are not taken to avoid a rise of the concentration of AMP after removing liver tissue.
• special precautions e.g. freeze-clamping
• AMP-PK phosphorylates Ser-565 of hormone-sensitive lipase. This phosphorylation inhibits subsequent phosphorylation and activation of hormone-sensitive lipase by cA-PK (Garton et al., 179 Eur. J. Biochem 249, 1989). Phosphorylation of hormone-sensitive lipase by AMP-PK might thus block the action of lipolytic hormones (and release of free fatty acids and glycerol from fat cells) which act by way of cyclic AMP and cA-PK.
• AMP-PK has also been reported to be itself regulated by phosphorylation, which activates the enzyme, and by dephosphorylation which inactivates the enzyme. Nanomolar concentrations of fatty acyl-CoA were shown to stimulate the 'AMP-PK kinase', thus activating AMP-PK. Since the latter activation will result in inactivation of acetyl-
• CoA carboxylase it provides a mechanism whereby fatty acyl-CoA can exert feed-back inhibition on fatty acid synthesis.
• the studies of the AMP-PK system indicate that it plays an important role in regulating the levels of fatty acids and cholesterol in the body. That
• AMP-PK acts on both acetyl-CoA carboxylase and HMG-CoA reductase most likely explains why hepatic fatty acid and cholesterol synthesis are regulated in parallel in several situations (e.g.. both synthetic pathways peak at the same time of the day, both are inhibited by diets high in polyunsaturated fatty acids) .
• AICAriboside As described in detail below, we have discovered that the addition of the nucleoside, AICAriboside, to suspensions of isolated rat hepatocytes provokes an inactivation of both acetyl-CoA carboxylase and HMG-CoA reductase. AICAriboside is efficiently converted by phosphorylation into the corresponding nucleotide, AICAribotide or ZMP, in isolated rat hepatocytes (Vincent et al. , 40 Diabetes 1259, 1991, data not shown) and in vivo (data not shown) .
• ZMP can also be formed from AICA base administration followed by in vivo phosphoribosylation.
• ZMP can also be formed from AICA base administration followed by in vivo phosphoribosylation.
• 3 H 2 0 results in the labelling of NADPH. Utilization of the latter by fatty acid synthetase results in the formation of labelled fatty acids and triglycerides. Besides entering fatty acid synthesis, 3 H 2 0 can also enter the biosynthesis of cholesterol (at the level of HMG-CoA reductase) .
• Example 1 Effect of AICAriboside on fatty acid synthesis with endogenous substrates
• fatty acid synthesis can proceed from endogenous substrates, glycogen, and ketogenic amino acids. This endogenous fatty acid synthesis is completely inhibited by 500 ⁇ M
• AICAriboside inhibits fatty acid synthesis from 15 mM glucose in a dose-dependent fashion (Fig. 3) . Half maximal inhibition is obtained with about 50 ⁇ M AICAriboside.
• AICAriboside inhibits fatty acid synthesis from lactate 10 M/pyruvate 1 mM (Fig. 4) .
• Fatty acid synthesis from lactate/pyruvate seems to be slightly less sensitive to AICAriboside than that from glucose (half- maximal inhibition with about 75 ⁇ M AICAriboside) .
• Example 4 Effect of AICAriboside on fatty acid synthesis with ketogenic amino acids
• Ketogenic amino acids enter fatty acid synthesis at the level of acetyl-CoA, thus bypassing the transport of pyruvate into the mitochondria, and the enzymes pyruvate dehydrogenase and pyruvate carboxylase.
• ketogenic amino acids are thought to be first deaminated in muscle, and to be transported thereafter to the liver in the form of ketoacids.
• fatty acid synthesis from leucine was compared with that from its transamination product, 2-ketoisocaproic acid.
• fatty acid synthesis with both substrates is completely inhibited by AICAriboside 500 ⁇ M.
• Example 5 Effect of AICAriboside on the activity of acetyl-CoA carboxylase
• Acetyl-CoA carboxylase is the limiting step of fatty acid synthesis. It is interconvertible by phosphorylation/dephosphorylation, the active form being dephosphorylated. Acetyl-CoA carboxylase is activated by a dephosphorylating phosphatase and inactivated by several kinases (including cAMP-dependent protein kinase, under the influence of glucagon) . In addition, inactivation of acetyl-CoA carboxylase by an AMP-activated protein kinase has been reported by Dr. Hardie's group. Fig. 7 shows that acetyl-CoA carboxylase (assay performed by the method of Bijleveld & Geelen, 918 Bioc. Biop. Acta 274, 1987) is inactivated by the addition of AICAriboside 500 ⁇ M. This suggests that ZMP acts at the level of the AMP-activated protein.
• Example 6 Effects on the incorporation of 3 H-,0 in the non-saponifiable lipid fraction
• ZMP by activating AMP-activated protein kinase, inactivates both acetyl-CoA carboxylase and HMG-CoA reductase, the limiting enzymes of, respectively, fatty acid and cholesterol synthesis.
• HMG-CoA reductase is the limiting step of cholesterol synthesis. It is interconvertible by phosphorylation/dephosphorylation, the active form being dephosphorylated. HMG-CoA reductase is activated by the dephosphorylating phosphatases, protein phosphatase 2A and 2C, and inactivated by several protein kinases. These include Ca 2 +/calmodulin-dependent protein kinase, protein kinase C, and as also described by Dr. Hardie's group. AMP-activated protein kinase. Fig.
• Example 8 Effect of ZMP on the activity of AMP-activated protein kinase
• Dr. Hardie and co-workers have set up a specific and sensitive assay of AMP-activated protein kinase. It is based on the incorporation of radioactivity from [y- 32 P]ATP into a 15-amino acid peptide, termed the SAMS peptide, designed after the sequence of acetyl-CoA carboxylase surrounding Ser79, the site which is phosphorylated exclusively by the AMP-activated protein kinase.
• SAMS peptide 15-amino acid peptide
• Fig. 11 shows that in this assay, ZMP stimulates up to nearly 8-fold the activity of rat liver AMP-activated protein kinase, partially purified up to the DEAE-Sepharose step as described by Davies et al. (Eur. J. Biochem. 186: 123-8, 1989). Half-maximal stimulation is obtained at 0.6 mM, and maximal stimulation at 4mM ZMP.
• Fig. 12 shows that 2mM ZMP overrides the stimulatory effect of concentrations of AMP below 0.1 mM, but is not additive and even slightly inhibitory at higher concentrations of AMP, suggesting that both nucleotides bind to the same site.
• Fig. 12 shows that 2mM ZMP overrides the stimulatory effect of concentrations of AMP below 0.1 mM, but is not additive and even slightly inhibitory at higher concentrations of AMP, suggesting that both nucleotides bind to the same site.

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