Regional and subcellular distribution of enzymes of branched-chain amino acid metabolism in brains of normal and diabetic rats

1985 ◽  
Vol 63 (10) ◽  
pp. 1234-1238 ◽  
Author(s):  
Margaret E. Brosnan ◽  
Ann Lowry ◽  
Yasmin Wasi ◽  
Martin Lowry ◽  
John T. Brosnan
Keyword(s):  
Amino Acid ◽  
Subcellular Distribution ◽  
Brain Homogenate ◽  
Total Activity ◽  
Brain Regions ◽  
Diabetic Rats ◽  
Whole Brain ◽  
Branched Chain Amino Acid ◽  
Branched Chain ◽  
Ketoacid Dehydrogenase

Branched-chain-amino-acid:α-ketoglutarate transaminase and branched-chain α-ketoacid dehydrogenase have been assayed in brains of control and of streptozotocin-induced diabetic rats. Enzyme activities were measured in five distinct regions of the brain: cerebellum, pons + medulla, midbrain, thalamus + hypothalamus, and telencephalon. Subcellular distribution of these enzymes in whole brain was assessed by fractionating brain homogenate into cytoplasm, free mitochondria, and synaptosomes. The following enzymes were used as markers: lactate dehydrogenase for cytoplasm, glutamate dehydrogenase for mitochondria, and glutamate decarboxylase for synaptosomes. The activity of the branched-chain amino acid transaminase in all brain regions was considerably higher than that of the branched-chain α-ketoacid dehydrogenase. While the highest activity of the transaminase occurred in brain-stem regions, the highest activity of the dehydrogenase was present in cerebellum and telencephalon. Diabetes did not affect the activity of the transaminase, but it caused a decrease in the total activity of the dehydrogenase in midbrain and in thalamus + hypothalamus. The transaminase was localized in the cytoplasmic fraction of whole brain, while the dehydrogenase was enriched in the free mitochondria.

scholarly journals Tissue-specific responses of branched-chain alpha-ketoacid dehydrogenase activity in metabolic acidosis.

1998 ◽  
Vol 9 (10) ◽  
pp. 1892-1898
Author(s):  
S R Price ◽  
X Wang ◽  
J L Bailey
Keyword(s):  
Amino Acid ◽  
Whole Body ◽  
Tissue Specific ◽  
Subunit Mrna ◽  
Branched Chain Amino Acid ◽  
Leucine Catabolism ◽  
Branched Chain ◽  
Ketoacid Dehydrogenase ◽  
Rate Limiting ◽  
Adrenalectomized Rats

In adrenalectomized rats, acidosis does not increase whole-body leucine oxidation unless a physiologic amount of glucocorticoids (dexamethasone) is also provided; an equivalent dose of dexamethasone without acidosis does not change leucine catabolism. Because the influences of acidification and glucocorticoids on branched-chain amino acid metabolism in specific organs are unknown, the function of branched-chain alpha-ketoacid dehydrogenase (BCKAD), the rate-limiting enzyme in branched-chain amino acid catabolism, in adrenalectomized rat skeletal muscle and liver, the two major tissues that degrade branched-chain amino acid was measured. In muscle of acidotic adrenalectomized rats receiving dexamethasone, basal and total BCKAD activities were increased 2.6- (P < 0.05) and 2.8-fold (P < 0.05), respectively. Neither acidosis nor dexamethasone alone increased these activities. BCKAD E1alpha subunit mRNA in muscle of acidotic rats given dexamethasone was increased 1.89-fold (P < 0.05) in parallel with the change in BCKAD activity; BCKAD E2 subunit mRNA was increased by acidosis, dexamethasone, or a combination of both stimuli. In contrast, basal BCKAD activity in liver of rats with acidosis or dexamethasone was nearly threefold lower (P < 0.05) and changes in enzyme activity reflected reduced subunit mRNA. Thus, there are reciprocal, tissue-specific changes in BCKAD function in response to acidosis.

Effect of alpha-ketoacid dehydrogenase phosphorylation on branched-chain amino acid metabolism in muscle

1991 ◽  
Vol 261 (5) ◽  
pp. E628-E634 ◽  
Author(s):  
D. A. Hood ◽  
R. L. Terjung
Keyword(s):  
Skeletal Muscle ◽  
Amino Acid ◽  
Energy Demand ◽  
Mitochondrial Content ◽  
Branched Chain Amino Acid ◽  
Branched Chain ◽  
Ketoacid Dehydrogenase ◽  
Fold Activation

The regulation of leucine and valine metabolism was evaluated in skeletal muscle of perfused rat hindlimb. Control of the branched-chain alpha-ketoacid dehydrogenase (BCKADH) via phosphorylation was removed with 0.4 mM alpha-chloroisocaproate (CIC). CIC activated the BCKADH complex 13- to 26-fold and led to increased rates of leucine and valine uptake into muscle, transamination to the corresponding alpha-ketoacid, and leucine (3- to 4-fold) and valine (6-fold) decarboxylation but led to decreased rates of alpha-ketoacid efflux from muscle. Although the increased rates of branched-chain amino acid (BCAA) decarboxylation were extensive, they were far below the extent of BCKADH activation as measured in vitro, suggesting that factors other than BCKADH activation become dominant in controlling the flux through alpha-ketoacid decarboxylation in skeletal muscle in situ. When the BCKADH capacity of muscle was increased 70–90% by a training-induced increase in mitochondrial content, the same 13- to 26-fold activation of the complex by CIC led to a rate of BCAA decarboxylation, which was only marginally greater (10–20%; P less than 0.05) than that of normal muscle. In addition, increasing the energy demand via muscle contractions led to a significant increase in leucine decarboxylation in the presence of complete activation of BCKADH by dephosphorylation. Thus BCKADH phosphorylation-dephosphorylation plays an important though not exclusive role in modulating the rates of BCAA metabolism in skeletal muscle. Differences in valine and leucine metabolism were apparent as valine catabolism bolstered citric acid cycle contents by increasing malate in red muscle with high mitochondrial content.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Mechanisms contributing to muscle-wasting in acute uremia: activation of amino acid catabolism.

1998 ◽  
Vol 9 (3) ◽  
pp. 439-443
Author(s):  
S R Price ◽  
D Reaich ◽  
A C Marinovic ◽  
B K England ◽  
J L Bailey ◽  
...  
Keyword(s):  
Amino Acid ◽  
Muscle Wasting ◽  
Essential Amino Acids ◽  
Mrna Levels ◽  
Amino Acid Catabolism ◽  
Metabolic Defects ◽  
Branched Chain Amino Acid ◽  
Branched Chain ◽  
Ketoacid Dehydrogenase ◽  
And Control

Acute uremia (ARF) causes metabolic defects in glucose and protein metabolism that contribute to muscle wasting. To examine whether there are also defects in the metabolism of essential amino acids in ARF, we measured the activity of the rate-limiting enzyme for branched-chain amino acid catabolism, branched-chain ketoacid dehydrogenase (BCKAD), in rat muscles. Because chronic acidosis activates muscle BCKAD, we also evaluated the influence of acidosis by studying ARF rats given either NaCl (ARF-NaCl) or NaHCO3 (ARF-HCO3) to prevent acidosis, and sham-operated, control rats given NaHCO3. ARF-NaCl rats became progressively acidemic (serum [HCO3] = 21.3 +/- 0.7 mM within 18 h and 14.7 +/- 0.8 mM after 44 h; mean +/- SEM), but this was corrected with NaHCO3. Plasma valine was low in ARF-NaCl and ARF-HCO3 rats. Plasma isoleucine, but not leucine, was low in ARF-NaCl rats, and isoleucine tended to be lower in ARF-HCO3 rats. Basal BCKAD activity (a measure of active BCKAD in muscle) was increased more than 17-fold (P < 0.01) in ARF-NaCl rat muscles, and this response was partially suppressed by NaHCO3. Maximal BCKAD activity (an estimate of BCKAD content), subunit mRNA levels, and BCKAD protein content were not different in ARF and control rat muscles. Thus, ARF increases branched-chain amino acid catabolism by activating BCKAD by a mechanism that includes acidosis. Moreover, in a muscle-wasting condition such as ARF, there is a coordinated increase in protein and essential amino acid catabolism.

Branched-chain amino acid metabolism in rat muscle: abnormal regulation in acidosis

1987 ◽  
Vol 252 (6) ◽  
pp. E712-E718 ◽  
Author(s):  
R. C. May ◽  
Y. Hara ◽  
R. A. Kelly ◽  
K. P. Block ◽  
M. G. Buse ◽  
...  
Keyword(s):  
Metabolic Acidosis ◽  
Amino Acid ◽  
Acid Metabolism ◽  
Muscle Protein ◽  
Total Activity ◽  
Keto Acid ◽  
Acid Dehydrogenase ◽  
Branched Chain Amino Acid ◽  
Pathological Conditions ◽  
Branched Chain

Branched-chain amino acid (BCAA) metabolism is frequently abnormal in pathological conditions accompanied by chronic metabolic acidosis. To study how metabolic acidosis affects BCAA metabolism in muscle, rats were gavage fed a 14% protein diet with or without 4 mmol NH4Cl X 100 g body wt-1 X day-1. Epitrochlearis muscles were incubated with L-[1-14C]-valine and L-[1-14C]leucine, and rates of decarboxylation, net transamination, and incorporation into muscle protein were measured. Plasma and muscle BCAA levels were lower (P less than 0.05) in acidotic rats. Rates of valine and leucine decarboxylation and net transamination were higher (P less than 0.05) in muscles from acidotic rats; these differences were associated with a 79% increase in the total activity of branched-chain alpha-keto acid dehydrogenase and a 146% increase in the activated form of the enzyme. We conclude that acidosis affects the regulation of BCAA metabolism by enhancing flux through the transaminase and by directly stimulating oxidative catabolism through activation of branched-chain alpha-keto acid dehydrogenase.

Rat muscle branched-chain ketoacid dehydrogenase activity and mRNAs increase with extracellular acidemia

1995 ◽  
Vol 268 (6) ◽  
pp. C1395-C1400 ◽  
Author(s):  
B. K. England ◽  
S. Greiber ◽  
W. E. Mitch ◽  
B. A. Bowers ◽  
W. J. Herring ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Amino Acid ◽  
Fold Increase ◽  
Maximal Activity ◽  
Amino Acid Catabolism ◽  
Branched Chain Amino Acid ◽  
Reticulocyte Lysate ◽  
Branched Chain ◽  
Ketoacid Dehydrogenase ◽  
Rate Limiting

The rate-limiting enzyme in branched-chain amino acid catabolism is branched-chain ketoacid dehydrogenase (BCKAD). In rats fed NH4Cl to induce acidemia, we find increased basal BCKAD activity as well as maximal activity in skeletal muscle. Concurrently, there is a > 10-fold increase in mRNAs of BCKAD subunits in skeletal muscle plus an increase in cardiac muscle but not in liver or kidney. There was no increase in mRNA for malate dehydrogenase or for cytosolic glyceraldehyde-3-phosphate dehydrogenase. Evaluation of the translation capacity of BCKAD mRNAs in muscle of acidemic rats yielded more immunoreactive BCKAD whether the proteins were synthesized from muscle RNA using rabbit reticulocyte lysate or directly using postmitochondrial homogenates. Although the RNA from muscle of acidemic rats yielded twice as much BCKAD protein, we found no net increase in mitochondrial BCKAD protein in muscle by Western blotting. Because there is increased proteolysis in muscle of rats with acidemia, the increase in mRNA might be a mechanism to augment BCKAD synthesis and activity in muscle.

Sign in / Sign up

Export Citation Format

Share Document