Coordinate Regulation of Malonyl-CoA Decarboxylase,sn-Glycerol-3-phosphate Acyltransferase, and Acetyl-CoA Carboxylase by AMP-activated Protein Kinase in Rat Tissues in Response to Exercise

Abstract

Changes in the concentration of malonyl-CoA in many tissues have been related to alterations in the activity of acetyl-CoA carboxylase (ACC), the rate-limiting enzyme in its formation. In contrast, little is known about the physiological role of malonyl-CoA decarboxylase (MCD), an enzyme responsible for malonyl-CoA catabolism. In this study, we examined the effects of voluntary exercise on MCD activity in rat liver, skeletal muscle, and adipose tissue. In addition, the activity ofsn-glycerol-3-phosphate acyltransferase (GPAT), which like MCD and ACC can be regulated by AMP-activated protein kinase (AMPK), was assayed. Thirty min after the completion of a treadmill run, MCD activity was increased ∼2-fold, malonyl-CoA levels were reduced, and ACC and GPAT activities were diminished by 50% in muscle and liver. These events appeared to be mediated via activation of AMPK since: 1) AMPK activity was concurrently increased by exercise in both tissues; 2) similar findings were observed after the injection of 5-amino 4 imidazole carboxamide, an AMPK activator; 3) changes in the activity of GPAT and ACC paralleled that of MCD; and 4) the increase in MCD activity in muscle was reversed in vitro by incubating immunoprecipitated enzyme from the exercised muscle with protein phosphatase 2A, and it was reproduced by incubating immunopurified MCD from resting muscle with purified AMPK. An unexpected finding was that exercise caused similar changes in the activities of ACC, MCD, GPAT, and AMPK and the concentration of malonyl-CoA in adipose tissue. In conclusion: MCD, GPAT, and ACC are coordinately regulated by AMPK in liver and adipose tissue in response to exercise, and except for GPAT, also in muscle. The results suggest that AMPK activation plays a major role in regulating lipid metabolism in many cells following exercise. They also suggest that in each of them, it acts to increase fatty acid oxidation and decrease its esterification. Changes in the concentration of malonyl-CoA in many tissues have been related to alterations in the activity of acetyl-CoA carboxylase (ACC), the rate-limiting enzyme in its formation. In contrast, little is known about the physiological role of malonyl-CoA decarboxylase (MCD), an enzyme responsible for malonyl-CoA catabolism. In this study, we examined the effects of voluntary exercise on MCD activity in rat liver, skeletal muscle, and adipose tissue. In addition, the activity ofsn-glycerol-3-phosphate acyltransferase (GPAT), which like MCD and ACC can be regulated by AMP-activated protein kinase (AMPK), was assayed. Thirty min after the completion of a treadmill run, MCD activity was increased ∼2-fold, malonyl-CoA levels were reduced, and ACC and GPAT activities were diminished by 50% in muscle and liver. These events appeared to be mediated via activation of AMPK since: 1) AMPK activity was concurrently increased by exercise in both tissues; 2) similar findings were observed after the injection of 5-amino 4 imidazole carboxamide, an AMPK activator; 3) changes in the activity of GPAT and ACC paralleled that of MCD; and 4) the increase in MCD activity in muscle was reversed in vitro by incubating immunoprecipitated enzyme from the exercised muscle with protein phosphatase 2A, and it was reproduced by incubating immunopurified MCD from resting muscle with purified AMPK. An unexpected finding was that exercise caused similar changes in the activities of ACC, MCD, GPAT, and AMPK and the concentration of malonyl-CoA in adipose tissue. In conclusion: MCD, GPAT, and ACC are coordinately regulated by AMPK in liver and adipose tissue in response to exercise, and except for GPAT, also in muscle. The results suggest that AMPK activation plays a major role in regulating lipid metabolism in many cells following exercise. They also suggest that in each of them, it acts to increase fatty acid oxidation and decrease its esterification. acetyl-CoA carboxylase malonyl-CoA decarboxylase sn-glycerol-3-phosphate acyltransferase AMP-activated protein kinase 5-amino 4-imidazolecarboxamide riboside protein phosphatase 2A Malonyl-CoA, in addition to being an intermediate in the de novo synthesis of fatty acids, is an inhibitor of carnitine palmitoyltransferase I, the enzyme that regulates the transfer of long-chain fatty acyl-CoA into mitochondria, where they are oxidized (1McGarry J.D. Biochem. Soc. Trans. 1995; 23: 321-324Crossref PubMed Scopus (101) Google Scholar). One factor governing the concentration of malonyl-CoA is acetyl-CoA carboxylase (ACC),1 the rate-limiting enzyme in its synthesis. ACC is subject to both allosteric and covalent (by phosphorylation) regulation, and in some tissues, to changes in its abundance. A multitude of studies in such tissues as liver and muscle have clearly shown that increases and decreases in malonyl-CoA levels correlate closely with changes in ACC activity (2McGarry J.D. Mills S.E. Long C.S. Foster D.W. Biochem. J. 1983; 214: 21-28Crossref PubMed Scopus (466) Google Scholar, 3Winder W.W. Maclean P.S. Lucas J.C. Fernley J.E. Tumble G.E. J. Appl. Physiol. 1995; 78: 578-582Crossref PubMed Scopus (5) Google Scholar, 4Vavvas D. Apazidis A Saha A.K. Gamble J. Patel A. Kemp B.E. Witters L.A. Ruderman N.B. J. Biol. Chem. 1997; 272: 13255-13261Abstract Full Text Full Text PDF PubMed Scopus (348) Google Scholar). It is less clear whether malonyl-CoA decarboxylase (MCD), an enzyme that degrades malonyl-CoA, also regulates its concentration under physiological conditions. Recent studies suggest that the concentration of malonyl-CoA in liver and muscle in certain circumstances correlates inversely with changes in MCD activity. Thus, increases in MCD activity have been observed in rat liver during starvation (5Dyck J.R. Berthainme L.G. Thomas P.D. Kautor P.F. Barr A.J. Barr R. Singh D. Hopkins T.A. Voilley N. Prentki M. Lopaschuk G.D. Biochem. J. 2000; 350: 599-608Crossref PubMed Scopus (61) Google Scholar) and in skeletal muscle (6Saha A.K. Schwarsin A.J. Roduit R. Masse F. Kaushik V. Tornheim K. Prentki M. Ruderman N.B. J. Biol. Chem. 2000; 275: 24279-24283Abstract Full Text Full Text PDF PubMed Scopus (168) Google Scholar) in response to electrically induced contractions. In the latter situation, the increase in activity was attributable to activation of AMP-activated protein kinase (AMPK), an enzyme that also phosphorylates and inhibits ACC. Despite this, the physiological role of MCD in regulating the concentration of malonyl-CoA remains open to question as are the mechanisms by which its activity is regulated (7Habinowski S.A. Hirshman M. Sakamoto K. Kemp B.E. Gould S.J. Goodyear L.J. Witters L.A. Arch. Biochem. Biophys. 2001; 396: 71-79Crossref PubMed Scopus (40) Google Scholar). The present study explores the effect of voluntary exercise on MCD activity in rat liver, skeletal muscle, and adipose tissue and how observed changes relate temporally to alterations in the activities of ACC, AMPK, and glycerophosphate acyltransferase (GPAT), another enzyme shown previously to be regulated by AMPK (16Muoio D.M. Seefeld K. Witters L.A. Coleman R.A. Biochem. J. 1999; 338: 783-791Crossref PubMed Scopus (345) Google Scholar) and malonyl-CoA concentration. In addition, the response to exercise was compared with that following the administration in vivo of the AMPK activator 5-amino 4-imidazolecarboxamide riboside (AICAR), and in skeletal muscle, the effect of purified AMPK on MCD activity was examined in vitro. Finally, since it has recently been suggested that measurements of MCD activity may vary with the assay used (7Habinowski S.A. Hirshman M. Sakamoto K. Kemp B.E. Gould S.J. Goodyear L.J. Witters L.A. Arch. Biochem. Biophys. 2001; 396: 71-79Crossref PubMed Scopus (40) Google Scholar), in some studies, results obtained with spectrophotometric and radiometric methods were compared. Male Sprague-Dawley rats, weighing ∼245–275 g, were obtained from Charles River Laboratories (Wilmington, MA). They were randomly distributed into two groups designated rest and exercise. All rats were run for 5 min/day at 15 m/min up a 30% grade on a rodent treadmill (Economical Exercise Treadmill Model Exer-4, Columbus Instruments International Corporation, Columbus, OH) for 1 week to acclimate them to handling and to running on the treadmill. They were housed in individual cages in a temperature-controlled room (22 ± 1 °C) on a 12:12 h light-dark cycle and provided water and Purina rat chowad libitum. On the day of experimentation, one group remained sedentary, and the other ran on a rodent treadmill at 21 m/min up a 12% grade for 30 min. All rats were then injected intraperitoneally with sodium pentobarbital (6 mg/100 g of body weight) at rest or immediately after exercise. Subsequently, samples of blood were taken via orbital sinus puncture; the gastrocnemius muscle, liver, and white adipose tissue were excised and immediately frozen in liquid nitrogen; and the rats were sacrificed by exsanguination. Male Sprague-Dawley rats, weighing 320-360 g, were obtained from Charles River Laboratories. They were fedad libitum and maintained in a temperature-controlled animal facility with light-dark cycles of 8:00 a.m. to 8:00 p.m. Food intake was monitored. Body weight was assessed weekly at time of day. Rats were anesthetized and sacrificed between 11 a.m. and 1 p.m., 2 h after AICAR (250 mg/kg of body weight) injection. Control rats were injected with a comparable volume of saline. Plasma insulin was measured by radioimmunoassay with a rat insulin standard (Linco Research, St. Charles, MO), and plasma glucose was determined by the hexokinase method (8Lowry O.H. Passonneau J.V. A Flexible System of Enzymatic Analysis. Academic Press, New York1972: 174-177Google Scholar). Malonyl-CoA in muscle and liver was measured by the radioisotopic method described by McGarry et al. (9McGarry J.D. Stark M.J. Foster D.W. J. Biol. Chem. 1978; 253: 8291-8293Abstract Full Text PDF PubMed Google Scholar) as modified in our laboratory (10Chien D. Dean D Saha A.K. Flatt J.P. Ruderman N.B. Am. J. Physiol. 2000; 279: E259-E265Crossref PubMed Google Scholar, 11Saha A.K. Kurowski T.G. Ruderman N.B. Am. J. Physiol. 1995; 269: E283-E289PubMed Google Scholar). Adipose tissue malonyl-CoA was determined by the same method after treatment of the perchloric acid tissue extract with chloroform/methanol to remove lipid as described by Denton and Biochem. J. PubMed Scopus Google Scholar). of MCD in liver and adipose tissue was by a of the method of et J.R. Berthainme L.G. Thomas P.D. Kautor P.F. Barr A.J. Barr R. Singh D. Hopkins T.A. Voilley N. Prentki M. Lopaschuk G.D. Biochem. J. 2000; 350: 599-608Crossref PubMed Scopus (61) Google Scholar). frozen liver or adipose tissue was in liquid and of tissue was in a in 30 of a of 2 5 5 5 4 and 1 were then at 5 min at 4 A volume of was for of protein concentration by the method of M. Biochem. PubMed Scopus Google Scholar) with as the MCD was purified from the by was The was for 1 h at 4 and then at g for min at 4 The from this was and with was The was then at for min at 4 and the was in and at 4 assayed. g for 5 min at 4 °C) from frozen of were purified by as described previously (6Saha A.K. Schwarsin A.J. Roduit R. Masse F. Kaushik V. Tornheim K. Prentki M. Ruderman N.B. J. Biol. Chem. 2000; 275: 24279-24283Abstract Full Text Full Text PDF PubMed Scopus (168) Google Scholar). from with the of MCD, which both and was used N. Roduit R. R. J.R. Lopaschuk G.D. Prentki M. Biochem. J. 1999; PubMed Scopus Google Scholar). In one study, a MCD the of the enzyme with a was also In studies, MCD activity was measured a (6Saha A.K. Schwarsin A.J. Roduit R. Masse F. Kaushik V. Tornheim K. Prentki M. Ruderman N.B. J. Biol. Chem. 2000; 275: 24279-24283Abstract Full Text Full Text PDF PubMed Scopus (168) Google Scholar). The and were at and to a In addition, the was at to the A was in a by and was then and was to the was was and another was Subsequently, the immunopurified enzyme or the enzyme purified by was and the of was measured from the in each an malonyl-CoA was used as a are of protein in the g tissue A radiometric MCD assay N. Roduit R. R. J.R. Lopaschuk G.D. Prentki M. Biochem. J. 1999; PubMed Scopus Google Scholar) was also used for of MCD activity. The of the muscle was for min in the standard The was by perchloric and the were by The of by the MCD into was determined by in which was to with and then was to the to with the acetyl-CoA to In the of the and were by the into a of and the at for min. MCD as of acetyl-CoA of muscle was by with acetyl-CoA and liver for AMPK were as described by Kaushik et al. Dean Kurowski T.G. Saha A.K. Ruderman N.B. Am. J. Physiol. 2001; PubMed Google Scholar). AMPK was immunoprecipitated from a g of muscle and liver with or with the or of the AMPK were then on and The enzyme was as described previously D. Apazidis A Saha A.K. Gamble J. Patel A. Kemp B.E. Witters L.A. Ruderman N.B. J. Biol. Chem. 1997; 272: 13255-13261Abstract Full Text Full Text PDF PubMed Scopus (348) Google Scholar). In of was to the and of the was then on which was with sodium It was to assay immunopurified AMPK activity in adipose tissue for AMPK activity in adipose tissue was determined in an as for the ACC ACC activity in muscle, liver, and adipose tissue was as described by et al. D. Apazidis A Saha A.K. Gamble J. Patel A. Kemp B.E. Witters L.A. Ruderman N.B. J. Biol. Chem. 1997; 272: 13255-13261Abstract Full Text Full Text PDF PubMed Scopus (348) Google Scholar). were to a under liquid The frozen was and then D. Apazidis A Saha A.K. Gamble J. Patel A. Kemp B.E. Witters L.A. Ruderman N.B. J. Biol. Chem. 1997; 272: 13255-13261Abstract Full Text Full Text PDF PubMed Scopus (348) Google Scholar). The was immediately at g for min. The ACC was from the by the addition of of and on for 30 min. The was then by at g for 30 and the was in of the volume of and to remove The was used for of ACC activity. acyltransferase was with and in the or of 1 to the as described by et al. (16Muoio D.M. Seefeld K. Witters L.A. Coleman R.A. Biochem. J. 1999; 338: 783-791Crossref PubMed Scopus (345) Google Scholar). are as the of into in the of (16Muoio D.M. Seefeld K. Witters L.A. Coleman R.A. Biochem. J. 1999; 338: 783-791Crossref PubMed Scopus (345) Google Scholar). were at 30 for min. GPAT was by activity from the was immunoprecipitated and at with or purified AMPK provided by where 1 1 of to the and and for time as in the for the protein kinase of the of protein and kinase of the rat liver kinase studies, the was the same as for AMPK. MCD activity was determined as described are as ± S.E. between groups were determined by the where was Malonyl-CoA levels and MCD, GPAT, and ACC activities were measured in tissues of rats and rats that run on a treadmill for 30 min. All samples were taken 30 min after the completion of the exercise. plasma glucose levels were in exercised in rats ± ± In contrast, plasma insulin levels to be in the exercised group ± ± the was The concentration of malonyl-CoA and the activity of ACC in the gastrocnemius muscle by 50% after treadmill running in with findings by et al. W.W. J. J. J. Appl. Physiol. PubMed Scopus Google Scholar, W.W. J. D. Am. J. Physiol. PubMed Google Scholar). malonyl-CoA decarboxylase activity was increased from ± of muscle protein at rest to ± after exercise A similar of events was observed in liver, in which exercise increased MCD activity and caused the concentration of malonyl-CoA and ACC activity to decrease by 50% and in adipose in which exercise increased MCD activity by and the concentration of malonyl-CoA and the activity of ACC by The effects of exercise on AMPK activity in the tissues are shown in The activities of both the and AMPK increased in response to exercise in both liver and muscle with in liver and in muscle In adipose in which we were to the individual AMPK activity was increased by 50% 2) GPAT activity in gastrocnemius muscle was by exercise. In contrast, liver GPAT activity was diminished by 50% after exercise, as was GPAT activity in adipose tissue Exercise GPAT activity in of the tissues examined it was shown that AICAR administration the concentration of malonyl-CoA in liver and muscle W.W. J. Appl. Physiol. 1999; PubMed Scopus Google Scholar, W.W. Am. J. Physiol. 1997; PubMed Google Scholar). In this study, we that the administration of AICAR (250 mg/kg of body weight) the concentration of malonyl-CoA in from ± to ± In addition, it caused in the activities of ACC, MCD, and GPAT in the tissues similar to observed 30 min after of treatment of tissues with AICAR on ACC, MCD, and GPAT ± ± ± ± ± ± ± ± ± ± ± ± ± ± rats were anesthetized and sacrificed between 11 a.m. and 1 p.m., 2 h after AICAR (250 mg/kg of body weight) injection. are ± S.E. from ACC, MCD, and GPAT activities are as of in a rats were anesthetized and sacrificed between 11 a.m. and 1 p.m., 2 h after AICAR (250 mg/kg of body weight) injection. are ± S.E. from ACC, MCD, and GPAT activities are as of that of immunopurified MCD from the gastrocnemius of a rat with purified AMPK to a increase in MCD activity by min. changes after of of immunopurified MCD with protein kinase and kinase also MCD to a and AMPK. MCD from the gastrocnemius muscle taken 30 min after the completion of the exercise were with protein phosphatase 2A the observed increase in enzyme activity was effect of was by the phosphatase inhibitor acid to the that the effect of with AMPK on the activity of immunopurified MCD between Thus, MCD activity was increased by in the and by in the gastrocnemius muscle in the of immunopurified MCD by AMPK in muscle in vitro. MCD from and was at for 2 h with or purified AMPK and for 2 The results are from in each of which were from the have previously that treatment with in vitro the increase in immunopurified MCD activity in rat muscle by or with AICAR (6Saha A.K. Schwarsin A.J. Roduit R. Masse F. Kaushik V. Tornheim K. Prentki M. Ruderman N.B. J. Biol. Chem. 2000; 275: 24279-24283Abstract Full Text Full Text PDF PubMed Scopus (168) Google Scholar). shown in an effect on MCD activity after exercise. also measured MCD activity by a radiometric assay in of muscle taken after 5 min of induced by of the MCD activity was increased in the electrically muscle ± ± of an increase in activity similar to that obtained previously a spectrophotometric assay was used A.K. Schwarsin A.J. Roduit R. Masse F. Kaushik V. Tornheim K. Prentki M. Ruderman N.B. J. Biol. Chem. 2000; 275: 24279-24283Abstract Full Text Full Text PDF PubMed Scopus (168) Google and The findings of this study are as 1) exercise, malonyl-CoA decarboxylase with acetyl-CoA carboxylase in regulating the concentration of malonyl-CoA in liver and adipose as as in muscle. 2) In tissues, the activities of MCD and ACC are coordinately regulated by AMPK. 3) GPAT activity is diminished in liver and adipose tissue after exercise, and this to be regulated by AMPK. 4) The effect of changes be to increase the oxidation of fatty and to esterification. studies have shown that the concentration of malonyl-CoA is in skeletal muscle after exercise as a of a decrease in ACC activity W.W. J. J. J. Appl. Physiol. PubMed Scopus Google Scholar, W.W. J. D. Am. J. Physiol. PubMed Google Scholar). They have also suggested that the latter results from activation of AMPK, which phosphorylates and inhibits ACC. The results of the present study that voluntary exercise also increases the activity of MCD and that this is to a in AMPK activity. Thus, at the same time that decreases in ACC activity and malonyl-CoA concentration and an increase in AMPK activity were observed in muscle min after a treadmill the activity of MCD was increased by The finding that the increase in MCD activity was reproduced by administration of AICAR in with this as is the that of immunopurified MCD from a muscle with purified AMPK a increase in MCD activity. a of ACC and MCD attributable to AMPK has also been observed in rat muscle to by of the in vivo and following of the rat muscle with the AMPK activator AICAR (6Saha A.K. Schwarsin A.J. Roduit R. Masse F. Kaushik V. Tornheim K. Prentki M. Ruderman N.B. J. Biol. Chem. 2000; 275: 24279-24283Abstract Full Text Full Text PDF PubMed Scopus (168) Google Scholar). with MCD from treatment of immunopurified enzyme from an exercised muscle with reversed the increase in MCD activity. increases in MCD and AMPK activity and decreases in ACC activity and malonyl-CoA concentration were also observed in liver and adipose tissue at 30 min after exercise. AMPK activity was increased in liver and at 30 min after exercise was since one changes in and levels at this time in tissues, they at in ACC activity and malonyl-CoA concentration with an increase in AMPK have been observed by and W.W. J. Physiol. 1999; PubMed Scopus Google Scholar) in rat liver immediately after the completion of a treadmill they a similar after 2 h of exercise W.W. J. Physiol. 1999; PubMed Scopus Google Scholar). MCD was measured were studies after the of the exercise as was is that changes in liver and adipose and also in muscle, are mediated by increases in which have been known to during exercise J. PubMed Google Scholar). In this et al. D. PubMed Scopus Google Scholar) have recently that a vivo an increase in AMPK activity in skeletal muscle that is by the In addition, and Denton S.E. Denton PubMed Scopus Google Scholar) have shown that with an increase in AMPK in and we have a similar effect of in skeletal muscle. A. and N. the the findings the that exercise via its on AMPK also effects on and in adipose tissue and liver as as muscle W.W. J. Appl. Physiol. 1999; PubMed Scopus Google Scholar, W.W. M. J. Appl. Physiol. 2000; PubMed Scopus Google Scholar, P.F. Am. J. Physiol. 2000; 279: PubMed Google Scholar). In this AMPK has been in the of the of in liver A. D. M. F. D. Biol. 2000; PubMed Scopus Google Scholar) and the glucose in muscle J. Physiol. 2000; PubMed Scopus Google Scholar). A finding in this study was that exercise also in a decrease in GPAT activity in liver and adipose tissue. An study by et D.M. Seefeld K. Witters L.A. Coleman R.A. Biochem. J. 1999; 338: 783-791Crossref PubMed Scopus (345) Google Scholar) of GPAT activity by AMPK is with this GPAT activity in muscle was diminished after exercise. this was a related to the that its activity was that in liver or adipose tissue remains to be A activity of GPAT in muscle was also by et al. (16Muoio D.M. Seefeld K. Witters L.A. Coleman R.A. Biochem. J. 1999; 338: 783-791Crossref PubMed Scopus (345) Google Scholar), suggested that this for to an effect of AICAR on GPAT activity in this tissue it synthesis. the results suggest that MCD, ACC, and GPAT are coordinately regulated by AMPK in liver, adipose and in muscle after exercise The effect of events be to fatty acid oxidation and its esterification. It has been known that both fatty acid oxidation and are in muscle during exercise F. Am. J. Physiol. Google Scholar) and that fatty acid oxidation in muscle is increased after exercise, the muscle glucose to its AMPK activation after exercise since it also increases glucose into muscle W.W. Am. J. Physiol. 1997; PubMed Google Scholar, Hirshman N. S.A. Witters L.A. Goodyear L.J. 2000; PubMed Scopus Google Scholar), and it synthesis Hirshman N. S.A. Witters L.A. Goodyear L.J. 2000; PubMed Scopus Google Scholar, Kurowski Kaushik V. M. Ruderman N.B. 2001; Scholar). The effects of AMPK activation in liver and adipose tissue after exercise are less one that it increases fatty acid oxidation and inhibits synthesis in both tissues F. Am. J. Physiol. Google Scholar, J. Am. J. Physiol. 253: Google Scholar). In adipose the latter effect fatty from for into the where it for the of muscle and liver. In an study, we that induced by of the caused a increase in MCD activity in rat gastrocnemius muscle (6Saha A.K. Schwarsin A.J. Roduit R. Masse F. Kaushik V. Tornheim K. Prentki M. Ruderman N.B. J. Biol. Chem. 2000; 275: 24279-24283Abstract Full Text Full Text PDF PubMed Scopus (168) Google Scholar). et al. (7Habinowski S.A. Hirshman M. Sakamoto K. Kemp B.E. Gould S.J. Goodyear L.J. Witters L.A. Arch. Biochem. Biophys. 2001; 396: 71-79Crossref PubMed Scopus (40) Google Scholar) a similar study in which they were to this They this to the that they a radiometric assay for MCD that was the spectrophotometric assay used by (5Dyck J.R. Berthainme L.G. Thomas P.D. Kautor P.F. Barr A.J. Barr R. Singh D. Hopkins T.A. Voilley N. Prentki M. Lopaschuk G.D. Biochem. J. 2000; 350: 599-608Crossref PubMed Scopus (61) Google Scholar, Am. J. Physiol. 1999; PubMed Google Scholar). we also observed increases in MCD activity following of the the radiometric method was used to assay The for the results in the two studies is it the that we MCD in a g et al. (7Habinowski S.A. Hirshman M. Sakamoto K. Kemp B.E. Gould S.J. Goodyear L.J. Witters L.A. Arch. Biochem. Biophys. 2001; 396: 71-79Crossref PubMed Scopus (40) Google Scholar) used a that may with the In with this and Am. J. Physiol. 1999; PubMed Google Scholar), increased MCD activity in and et al. (5Dyck J.R. Berthainme L.G. Thomas P.D. Kautor P.F. Barr A.J. Barr R. Singh D. Hopkins T.A. Voilley N. Prentki M. Lopaschuk G.D. Biochem. J. 2000; 350: 599-608Crossref PubMed Scopus (61) Google Scholar), observed changes in MCD activity in liver during starvation and both tissue for In MCD, ACC, and GPAT to be coordinately regulated following exercise by an increase in AMPK activity in liver and and except for GPAT, in muscle. changes both increase the oxidation of long-chain fatty and decrease for the synthesis of and other to be determined are the responsible for the increase in AMPK activity in the tissues and whether the increase in AMPK activity following exercise to changes in the of of lipid and other Witters of for purified AMPK.