scholarly journals The effect of starvation on branched-chain 2-oxo acid oxidation in rat muscle

1984 ◽  
Vol 219 (1) ◽  
pp. 253-260 ◽  
Author(s):  
A J M Wagenmakers ◽  
J H Veerkamp
Keyword(s):  
Amino Acid ◽  
Protein Degradation ◽  
Specific Radioactivity ◽  
Acid Oxidation ◽  
Oxidative Decarboxylation ◽  
Precursor Pool ◽  
Oxidation Rates ◽  
Branched Chain Amino Acid ◽  
Endogenous Protein ◽  
Branched Chain

Oxidative-decarboxylation rates of branched-chain amino acids in rat hemidiaphragm and of branched-chain 2-oxo acids in hemidiaphragm, soleus muscle and heart slices of 110-120 g rats were increased considerably by 3-4 days of starvation, when they were calculated from the specific radioactivity in the medium. When the supply from endogenous protein degradation to the oxidation-precursor pool was severely limited by transaminase inhibitors, oxidative-decarboxylation rates of branched-chain 2-oxo acids rose significantly. Since this apparent increase was relatively larger in preparations from fed rats than from 3-days-starved rats, the differences in oxidation rates with nutritional state became less or even not significant. With rat heart the smaller dilution of the oxidation precursor pool after starvation is in accordance with the reported decrease in protein breakdown. Since protein degradation increases with starvation in skeletal muscles, we suggest that the amino acid pool arising from protein degradation is more segregated from the oxidation precursor pool in muscles from starved than from fed rats. We conclude that starvation increases branched-chain amino acid and 2-oxo acid oxidation in skeletal and cardiac muscle considerably less than has been suggested by previous studies.

scholarly journals Two mechanisms produce tissue-specific inhibition of fatty acid oxidation by oxfenicine

1985 ◽  
Vol 227 (2) ◽  
pp. 651-660 ◽  
Author(s):  
T W Stephens ◽  
A J Higgins ◽  
G A Cook ◽  
R A Harris
Keyword(s):  
Fatty Acid ◽  
Amino Acid ◽  
Fatty Acid Oxidation ◽  
Carnitine Palmitoyltransferase ◽  
Partial Purification ◽  
Acid Oxidation ◽  
Branched Chain Amino Acid ◽  
Malonyl Coa ◽  
Carnitine Palmitoyltransferase I ◽  
Branched Chain

Oxfenicine [S-2-(4-hydroxyphenyl)glycine] is transaminated in heart and liver to 4-hydroxyphenylglyoxylate, an inhibitor of fatty acid oxidation shown in this study to act at the level of carnitine palmitoyltransferase I (EC 2.3.1.21). Oxfenicine was an effective inhibitor of fatty acid oxidation in heart, but not in liver. Tissue specificity of oxfenicine inhibition of fatty acid oxidation was due to greater oxfenicine transaminase activity in heart and to greater sensitivity of heart carnitine palmitoyltransferase I to inhibition by 4-hydroxyphenylglyoxylate [I50 (concentration giving 50% inhibition) of 11 and 510 microM for the enzymes of heart and liver mitochondria, respectively]. Branched-chain-amino-acid aminotransferase (isoenzyme I, EC 2.6.1.42) was responsible for the transamination of oxfenicine in heart. A positive correlation was found between the capacity of various tissues to transaminate oxfenicine and the known content of branched-chain-amino-acid aminotransferase in these tissues. Out of three observed liver oxfenicine aminotransferase activities, one may correspond to asparagine aminotransferase, but the major activity could not be identified by partial purification and characterization. As reported previously for malonyl-CoA inhibition of carnitine palmitoyltransferase I, 4-hydroxyphenylglyoxylate inhibition of this enzyme was found to be very pH-dependent. In striking contrast with the kinetics of malonyl-CoA inhibition, 4-hydroxyphenylglyoxylate inhibition was not affected by oleoyl-CoA concentration, but was partially reversed by increasing carnitine concentrations.

scholarly journals Branched-chain amino acid oxidation in relation to catabolic enzyme activities in rats given aprotein-free diet at different stages of development

1974 ◽  
Vol 32 (3) ◽  
pp. 615-623 ◽  
Author(s):  
R. D. Sketcher ◽  
W. P. T. James
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Female Rats ◽  
Acid Oxidation ◽  
Stages Of Development ◽  
Oxidation Rates ◽  
Acid Dehydrogenase ◽  
Stage Of Development ◽  
The Difference ◽  
Branched Chain

1. The capacity of animals to conserve branched-chain amino acids was assessed during 3 weeks on a protein-free (PF) diet in groups of female rats at three stages of development, i.e. at weaning (35 g), in a period of rapid growth (85 g) and at maturity (200 g).2. Leucine and valine oxidation was assessed by monitoring the evolution of 14CO2 from a tracer dose of the [1-14C]-labelled L-amino acid given intragastrically. Activities of the L-leucine:2-ketoglutarate aminotransferase (EC 2.6.1.6) and α-keto acid dehydrogenase enzymes in leucine and valine metabolism were also determined in muscle and liver at weekly intervals.3. All three groups of rats given a normal protein intake excreted the same proportion of the dose of labelled leucine and valine. In rats given PF diet there was a consistent reduction in 14CO2 output from both L-[1-14C]leucine and L-[1-14C]valine, but valine was not conserved as efficiently as leucine.4. Muscle dehydrogenase responded to a PF diet in all three groups of rats, but the most marked changes occurred in the youngest group. In addition, there was a decrease in hepatic dehydrogenase activities for leucine and valine catabolism in the weanling group; in older animals there was little change in the α-keto-isovalerate, but a consistent decrease in the activity of the α-keto-isocaproic acid dehydrogenase. The difference in the responsiveness of the dehydrogenases, therefore, matched the difference between leucine and valine oxidation rates in vivo.5. Weanling animals responded rather more efficiently than the older animals to the need to conserve amino acids and there was no evidence of a poorly developed system for adapting to PF intake at this early stage of development.6. Despite reduced catabolism of the amino acids, aminotransferase activities in liver and muscle rose in the first 1–2 weeks on a PF regimen. Aminotransferase activity as such is unlikely to control acid oxidation.

scholarly journals Branched-chain-amino-acid-preferring peptidase activity of the lobster multicatalytic proteinase (proteasome) and the degradation of myofibrillar proteins

1995 ◽  
Vol 306 (1) ◽  
pp. 285-291 ◽  
Author(s):  
D L Mykles ◽  
M F Haire
Keyword(s):  
Amino Acid ◽  
Myofibrillar Proteins ◽  
Significant Finding ◽  
Peptidase Activity ◽  
Multicatalytic Proteinase ◽  
Branched Chain Amino Acid ◽  
Endogenous Protein ◽  
Proteolytic Activities ◽  
Branched Chain

The multicatalytic proteinase (MCP or proteasome) is a large proteolytic complex that contains at least five catalytic components: the trypsin-like, chymotrypsin-like, peptidylglutamyl-peptide hydrolase (PGPH), branched-chain-amino-acid-preferring (BrAAP) and small-neutral-amino-acid-preferring activities. We have shown that brief heating of the lobster muscle proteasome activates a proteolytic activity that degrades casein and myofibrillar proteins and is distinct from the trypsin-like, chymotrypsin-like and PGPH components. Here we identify the BrAAP activity as a catalytic component involved in the initial degradation of myofibrillar proteins in vitro. This conclusion is based on the following. (1) The BrAAP component was activated by heat-treatment, whereas the other four peptidase activities were not. (2) The BrAAP and proteolytic activities showed similar sensitivities to cations and protease inhibitors: both were inhibited by 3,4-dichloroisocoumarin, chymostatin, N-ethylmaleimide and Mg2+, but were not affected by leupeptin, phenylmethanesulphonyl fluoride or Li+. (3) The BrAAP activity was inhibited most strongly by casein substrates and troponin; conversely, the troponin-degrading activity was inhibited by the BrAAP substrate. Another significant finding was that incubation of the heat-activated MCP in the presence of chymostatin resulted in the limited cleavage of troponin-T2 (45 kDa) to two fragments of 41 and 42 kDa; this cleavage was completely suppressed by leupeptin. These results suggest that under certain conditions the trypsin-like component can cleave endogenous protein.

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