scholarly journals Hepatic zonation of acetyl-CoA carboxylase activity

1990 ◽  
Vol 270 (3) ◽  
pp. 665-672 ◽  
Author(s):  
J L Evans ◽  
B Quistorff ◽  
L A Witters
Keyword(s):  
Specific Activity ◽  
Covalent Modification ◽  
Maximal Velocity ◽  
Acetyl Coa Carboxylase ◽  
Dependent Protein Kinase ◽  
Acetyl Coa ◽  
Carboxylase Activity ◽  
Protein Mass ◽  
Dependent Protein ◽  
Enzyme Specific Activity

The activities of several hepatic enzymes are preferentially zonated to the periportal or perivenous cells of the liver acinus. Employing dual-digitonin-pulse perfusion of rat liver in the study of acetyl-CoA carboxylase (ACC), we have identified a heretofore unrecognized feature of hepatic zonation, namely an intrahepatic gradient in enzyme specific activity. ACC activity shows a relative periportal localization in normally feeding rats, even when corrected for ACC protein mass. In contrast with results previously reported by us [Evans, Quistorff & Witters (1989) Biochem. J. 259, 821-829], the total mass of both hepatic ACC isoenzymes was not found to differ between the two hepatic zones in the present study. In perfusion eluates from fed animals, periportal ACC displays enhanced citrate reactivity and two kinetic components of acetyl-CoA reactivity; the largest periportal/perivenous gradient (5-fold) is accounted for by a species with a lower Km for acetyl-CoA. The zonal gradient in ACC maximal velocity, measured in eluates from fed rats, does not persist after ACC purification, although the isolated periportal enzyme, like dephosphorylated ACC, has a lower activation constant for citrate. Total ACC protein phosphatase activity is higher in periportal eluates, but no differences in the activities of either a 5′-AMP-activated ACC kinase or the cyclic-AMP-dependent protein kinase are noted between the hepatic zones. The induction of total hepatic ACC mass and specific activity, on fasting/refeeding with a high-carbohydrate diet, abolishes the periportal/perivenous activity gradient, largely owing to a selective activation of perivenous enzyme. Nutritional induction is also accompanied by a marked alteration in ACC acetyl-CoA kinetics and abolition of the gradient in total ACC phosphatase. These studies indicate that hepatic enzyme zonation, which is often attributed to differential expression of enzyme protein, may result from zonal variations in enzyme specific activity, owing to differences in allosteric regulation and/or covalent modification.

Regulation of fatty acid biosynthesis in rats by physical training

1984 ◽  
Vol 56 (4) ◽  
pp. 1060-1064 ◽  
Author(s):  
R. Scorpio ◽  
R. L. Rigsby ◽  
D. R. Thomas ◽  
B. D. Gardner
Keyword(s):  
Fatty Acid ◽  
Physical Training ◽  
Fatty Acid Biosynthesis ◽  
Male Rats ◽  
Maximal Velocity ◽  
Acetyl Coa Carboxylase ◽  
Acid Biosynthesis ◽  
Acetyl Coa ◽  
Carboxylase Activity ◽  
Hepatic Fatty Acid

Physical training in the form of long-term nonexhaustive daily exercise was studied as a means of regulating fatty acid biosynthesis. Male rats were required to swim for periods up to 90 min/day. The exercise was carried out 6 days/wk for approximately 11 wk. Hepatic fatty acid biosynthesis and acetyl-CoA carboxylase [acetyl-CoA: CO2 ligase (EC 6.4.1.2)] activities were compared with nonexercised rats. At the end of the training period the exercised rats had a lower rate of fatty acid biosynthesis activity and a lower rate of acetyl-CoA carboxylase activity. The difference in acetyl-CoA carboxylase activity was due to a change in maximal velocity with no significant change in the Michaelis constant for acetyl-CoA. Untrained rats were subjected to a single bout of exercise. They also exhibited lower rates of fatty acid biosynthesis and acetyl-CoA carboxylase activities compared with nonexercised rats. However, the lower rates of these enzyme activities were sustained longer in the physically trained rats compared with the exercised untrained rats after the cessation of exercise. These results implicate acetyl-CoA carboxylase as a control site in the regulation of hepatic fatty acid biosynthesis by both physical training and acute exercise in rats. Possible inhibitory mechanisms are discussed.

scholarly journals The short-term regulation of hepatic acetyl-CoA carboxylase during starvation and re-feeding in the rat

1991 ◽  
Vol 280 (3) ◽  
pp. 733-737 ◽  
Author(s):  
M R Munday ◽  
M R Milic ◽  
S Takhar ◽  
M J Holness ◽  
M C Sugden
Keyword(s):  
Protein Kinase ◽  
Rat Liver ◽  
Acetyl Coa Carboxylase ◽  
Short Term ◽  
Dependent Protein Kinase ◽  
Acetyl Coa ◽  
Plasma Insulin Concentration ◽  
Dependent Protein ◽  
Time Courses ◽  
Amp Activated Protein Kinase

Rapid inhibition of acetyl-CoA carboxylase (ACC) activity in rat liver in response to 6 h starvation and rapid re-activation in response to 2-6 h of re-feeding chow were shown to be due to changes in the expressed activity of existing enzyme. Decreases and increases in ACC concentration occurred at later stages of the transitions, i.e. 6-48 h starvation and 8-24 h re-feeding respectively. The decrease in expressed activity of ACC was due primarily to changes in its phosphorylation state, demonstrated by a significantly decreased Vmax. and significantly increased Ka for citrate of enzyme purified by avidin-Sepharose chromatography from 6 h- or 48 h-starved rats. These effects were totally reversed within 2-4 h of chow re-feeding. Changes in the activity of purified ACC closely correlated with reciprocal changes in the activity of AMP-activated protein kinase (AMP-PK) over the fed to starved to re-fed transition. Increases in the activity ratio of cyclic-AMP-dependent protein kinase in response to starvation lagged behind the increase in AMP-PK and the decrease in ACC activity. Changes in AMP-PK and ACC activities of rat liver closely correlated with changes in plasma insulin concentration in response to time courses of starvation and re-feeding.

scholarly journals Multiple-site phosphorylation of the 280 kDa isoform of acetyl-CoA carboxylase in rat cardiac myocytes: evidence that cAMP-dependent protein kinase mediates effects of β-adrenergic stimulation

1999 ◽  
Vol 341 (2) ◽  
pp. 347-354 ◽  
Author(s):  
Adrienne N. BOONE ◽  
Brian RODRIGUES ◽  
Roger W. BROWNSEY
Keyword(s):  
Protein Kinase ◽  
Ventricular Myocytes ◽  
Acetyl Coa Carboxylase ◽  
Adrenergic Stimulation ◽  
Dependent Protein Kinase ◽  
Acetyl Coa ◽  
Camp Dependent Protein Kinase ◽  
Malonyl Coa ◽  
Dependent Protein

Two major forms of mammalian acetyl-CoA carboxylase (EC 6.4.1.2), ACC-α and ACC-β, have been described and the sequences of the isoforms deduced. ACC-β is the predominant isoform expressed in heart and skeletal muscles, in which a major role of malonyl-CoA is probably to regulate fatty acid β-oxidation. The regulatory properties of ACC-β are incompletely defined but it is known that some cellular stresses lead to inhibition in parallel with the activation of AMP-activated protein kinase (AMP-PK). Here we examine the phosphorylation state of ACC-β within intact rat cardiac ventricular myocytes. Treatment of myocytes with the β-adrenergic agonist isoprenaline (isoproterenol) led to increased ACC-β phosphorylation that was maximal within 2 min and with 50 nM agonist. Effects of isoprenaline were revealed by the incorporation of 32P into ACC in cells incubated with [32P]Pi and also by a marked decrease (approx. 80%) in subsequent phosphorylation in vitro with cAMP-dependent protein kinase (PKA). Analysis of tryptic phosphopeptides revealed that ACC-β was phosphorylated at multiple sites by incubationin vitro with PKA or AMP-PK. Treatment of myocytes with isoprenaline affected all the major phosphorylation sites of ACC-β that were recognized in vitro by purified PKA, so that subsequent phosphorylation in vitro was greatly diminished after cell stimulation. β-Adrenergic stimulation led to decreases in cellular malonyl-CoA concentrations but no changes in kinetic properties of ACC were detected after cell homogenization and partial purification of proteins. The results suggest that: (1) ACC-β is rapidly phosphorylated at multiple sites within intact cardiac ventricular myocytes after β-adrenergic stimulation, (2) ACC-β is phosphorylated in vitro by PKA and AMP-PK at multiple sites, including at least one site accessible to each kinase, as well as kinase-selective sites, and (3) PKA is a physiologically significant ACC-β kinase.

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