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At least 19 recordsLinked to original sources

PubMed1979

Comparison of 15N-labelled glycine, aspartate, valine and leucine for measurement of whole-body protein turnover.

1. Whole-body protein turnover was measured in rats by constant infusion of 15N-labelled glycine, aspartate, valine and leucine and measuring the enrichment of hepatic and renal urea and ammonia nitrogen. 2. The values obtained with [15N]glycine were comparable with values reported with methods based on different assumptions. 3. [15N]Aspartate gave rise to an increased enrichment of urea and ammonia and hence to lower protein-turnover rates. 4. [15N]Valine and [15N]leucine gave low enrichments of nitrogenous end products and hence to high protein-turnover rates. 5. All 15N-labelled amino acids are not equally suitable for measuring whole-body protein turnover by the end-product method. The relative amounts of 15N going to the end products can be predicted from the known individual metabolism of aspartate and the branched-chain amino acids.

Ammonia↗

PubMed1977

Protein turnover, synthesis and breakdown before and after recovery from protein-energy malnutrition.

1. Rates of total protein turnover, synthesis and breakdown were measured in five children before and after recovery from severe protein-energy malnutrition and while receiving 0.6 g of protein and 397 kJ day-1 kg-1. 2. Thes rates were calculated after giving doses of [15N]glycine every 2 h along with the feeds and measuring the rate of excretion of [15N]urea in urine. 3. Malnourished children had significantly lower rates of protein turnover, synthesis and breakdown than after they had recovered. 4. During recovery from protein-energy malnutrition, two children on a daily intake of 1.2 g of protein and 605 J/kg body weight, had rates of protein turnover, synthesis and breakdown that were twice as great as those found on admission and higher than after recovery. 5. On the study diet the malnourished children maintained their weight while the recovered children lost weight; the apparent nitrogen balance was more positive in the malnourished children. 6. In recovered children, the rate of protein synthesis was unchanged over a wide range of protein intake, whereas the rate of protein breakdown appeared to rise with a reduction in protein intake.

Body Weight↗

PubMed1977

The relationship between dietary intake, weight change, nitrogen balance, and protein turnover in man.

We have examined the relationships between protein turnover, protein synthesis, and protein breakdown and dietary intake, weight change, and nitrogen balance in children who were recovering and had recovered from severe protein-energy-malnutrition. Protein metabolism was measured by giving [15N]glycine and measuring the enrichment of urinary urea. The level of dietary protein did not affect protein metabolism. There were highly significant correlations between both protein flux and protein synthesis and the ad libitum dietary intake, nitrogen balance, and weight change. Over the range of dietary intake, 60 to 270 cal/kg per day, the protein synthesis rate increased 5-fold. Large changes in dietary intake resulted in small changes in protein breakdown, with breakdown being least on an inadequate intake. Changes in the rate of protein breakdown did not contribute to changes in nitrogen balance or body weight.

Body Weight↗

PubMed1979

Protein turnover in the extreme thermophile Thermus aquaticus.

Protein turnover in the extreme bacterial thermophile Thermus aquaticus was examined in exponential cultures at 75 degrees C. The relative amount of [3H]leucine incorporated into trichloroacetic acid-insoluble material was stable in pulse-chase experiments assayed over 2.5 h. The trichloroacetic acid-insoluble radioactive leucine was stable upon the addition of chloramphenicol, which blocks protein synthesis in T. aquaticus. The specific activity of a phosphate-repressible alkaline phosphatase, investigated in the presence of chloramphenicol, did not decrease. The addition of excess orthophosphate to cultures derepressed for the alkaline phosphatase did not show a marked effect on the specific activity over a 2-h period. On the basis of these four experiments, it does not appear that a high protein turnover rate is essential for the thermophily of T. aquaticus at 75 degrees C.

Alkaline Phosphatase↗

PubMed1977

Relationships between intracellular proteolytic activity and protein turnover in Bacillus megaterium.

When incubated in a sporulation medium, the sporogenous strains of Bacillus megaterium degrade proteins at a rate of 4-10% X h-1. The maximal rate of protein turnover is reached after 3-4 hrs at the time of development of forespores and then decreases again. The rate of protein turnover in the asporogenous strain decreases steadily under similar conditions from 3-8% X h-1 at the beginning of incubation to 1% X h-1 after 5-6 hrs in the sporulation medium. The rate of degradation of proteins in vitro in protoplast lysates is similar or higher than the rate of protein turnover. The exocellular, as well as periplasmic proteolytic activity, is suppressed by amino acids more severely than the activity in protoplasts. Mutants devoid of the exocellular proteolytic enzyme contain also less proteolytic activity in the periplasm than in the protoplasts, in contrast to the wild strain. However, their rate of protein turnover, as well as the degradation of abnormal proteins is similar to that in the wild strain. This supports a view that the proteolytic system in protoplasts is involved in intracellular protein catabolism. The periplasmic enzyme can be considered as a kind of the exocellular proteinase.

Bacillus megaterium↗

PubMed1979

The relationship between protein turnover and energy balance in lean and genetically obese (ob/ob) mice.

1. Groups of lean and genetically obese (ob/ob) mice were adapted to varying energy intakes and the rates of total protein turnover in liver, gut and kidney were measured. 2. Lean mice gained less weight when fed above maintenance and lost less weight when fed below maintance than obese mice. 3. Hepatic protein turnover (mg/d) was sigmoidally related to digestible energy intake in lean mice but showed no significant changes with dietary intake in obese mice. 4. The changes in protein turnover resulted from changes in both the half-lives of protein synthesis and catabolism and in tissue protein content. 5. In the lean mice, protein turnover in kidney and gut was not significantly changed with increasing energy intake until the highest level was reached. 6. The findings suggest that protein turnover may be an important cycle for the regulation of energy balance in mice and that this cycle is impaired in the genetically obese (ob/ob) mice.

Animals↗

PubMed1979

A comparison of methods for the measurement of protein turnover in vivo.

Steady-state rates of turnover of two single proteins were measured in vivo by two independent methods. The fractional rate of synthesis of liver ornithine aminotransferase, measured by a continuous infusion of L-[2,6-3H]tyrosine, was 0.42 day-1, whereas in the same animals the fractional rate of degradation measured by loss of radioactivity from amino acids labelled via [14C]bicarbonate was 0.40 day-1. The agreement between methods confirms the reliability of each method for the study of hepatic protein turnover. In contrast, [14C]bicarbonate-labelled amino acids are extensively reutilized in muscle, and are therefore unsuitable for measuring rates of muscle protein breakdown.

Animals↗

PubMed1979

The effect of surgical trauma on muscle protein turnover in rats. A serious methodological misunderstanding.

The reported rates of protein degradation in a recent paper on the effect of surgical trauma on muscle protein turnover [Hoover-Plow & Clifford (1978) Biochem. J. 176, 137--142] have no real meaning because of a serious methodological misunderstanding by the authors. In addition, there are problems involved in the determination of synthesis rates, so that the reported effects of trauma on muscle protein turnover can be discounted.

Animals↗

PubMed1979

Effect of leucine and metabolites of branched chain amino acids on protein turnover in heart.

Leucine, but not isoleucine or valine, inhibited protein degradation and accelerated protein synthesis in hearts perfused with buffer that contained glucose (15 mM) and normal plasma levels of other amino acids, except for the branched chain compounds. Products of leucine, isoleucine, and valine metabolism also inhibited protein degradation and stimulated protein synthesis. These compounds included the transamination and decarboxylation products, as well as acetate, acetoacetate, and propionate. In some, but not all instances, inhibition of degradation and acceleration of synthesis were accompanied by an increase in intracellular leucine. When insulin was added to the perfusate, the rate of degradation was reduced by 40%, but addition of leucine was ineffective in the presence of the hormone. Insulin, leucine (2 mM) and a mixture of branched chain amino acids at normal plasma levels increased latency of cathepsin D in hearts that were perfused with buffer containing glucose. A combination of leucine and insulin increased latency more than either substance alone. These studies indicate that leucine as well as a variety of substrates that are oxidized in the citric acid cycle are involved in regulation of protein turnover in heart muscle.

Amino Acids↗

PubMed2026

An integrated proteomics and transcriptomics analysis highlights concordance between protein turnover and carbohydrate transport and metabolism as key functional categories during the growth of Trichophyton rubrum.

Dermatophytes are a class of keratinophilic skin fungi that invade host skin, hair, and nails to acquire nutrients. An integrated multi-omics approach utilizing liquid chromatography-tandem mass spectrometry and RNA-seq after growth in a protein-rich soy medium was employed to capture the major subset of secreted protein families of Trichophyton rubrum. The secretome consisted mainly of proteases and cell wall-degrading enzymes, with subtilisins (Sub6 and Sub7), metallopeptidase (LAP2), and chitinase having the most abundant peptides. Transcriptional profiling indicated fungal adaptation in protein-rich media to process the protein nutrients through modulation of metabolism and general cellular function pathways. Correlation analysis between proteomics and transcriptomics data using functional KOG categories shows high concordance of KOG categories O (posttranslational modification, protein turnover, and chaperones), P (inorganic ion transport and metabolism), and G (carbohydrate transport and metabolism), as per cosine similarity analysis.IMPORTANCEDermatophytes are keratinophilic skin fungal pathogens that invade host skin, hair, and nails to acquire nutrients. There is an epidemic-like increase in infections, as well as an increase in antimicrobial resistance among dermatophytes, as witnessed over the last decade. There is hence a need to understand the key pathways and virulence factors required during growth and infection. We present an integrated multi-omics analysis (proteomics and transcriptomics data) using a vector-based similarity approach to show high concordance of KOG functional categories belonging to posttranslational modification, protein turnover, carbohydrate transport, and metabolism.

Proteomics↗

PubMed1978

The effects of denervation on protein turnover of the soleus and extensor digitorum longus muscles of adult mice.

1. Changes in protein turnover of the soleus and EDL muscles of adult mice have been studied 1, 7 and 80 days after denervation. 2. Increased rates of protein degradation 7 and 80 days post-denervation correlated with the atrophy and loss of protein from these muscles. 3. Rates of protein synthesis in the EDL decreased 24 hr after nerve section. However, these synthetic rates increased again to become higher in the 7 day denervated muscles compared with their controls. These latter anabolic changes are inconsistent with the concept of a denervated muscle being inactive. 4. These findings have been compared with a similar study on muscles of growing rats. Any passive stretching of the denervated muscles by continued bone growth appears unlikely to be a crucial factor explaining the increased rates of protein synthesis 7 days after denervation.

Animals↗

PubMed1975

Regulation of mitochondrial protein turnover by thyroid hormone(s).

1. The effect of thyroidectomy on turnover rates of liver, kidney and brain mitochondrial proteins was examined. 2. In the euthyroid state, liver and kidney mitochondria show a synchronous turnover with all protein components showing more or less identical half-lives compared with the whole mitochondria. The brain mitochondrial proteins show asynchronous turnover, the soluble proteins having shorter half-lives. 3. Mitochondrial DNA (m-DNA) of liver and kidney has half-lives comparable with that of whole mitochondria from these tissues. 4. Thyroidectomy results in increased half-lives of liver and kidney mitochondria, with no apparent change in the half-life of brain mitochondria. 5. A detailed investigation of the turnover rates of several protein components revealed a significant decrease in the turnover rates of mitochondrial insoluble proteins from the three tissues under study. 6. The turnover rates of m-DNA of liver and kidney show a parallel decrease. 7. Thus it is apparent that thyroid hormone(s) may have a regulatory role in maintaining the synchrony of turnover of liver and kidney mitochondria in the euthyroid state. Turnover of brain mitochondria may perhaps be regulated by some other factor(s) in addition to thyroid hormone(s). 8. It seems likely that during mitochondrial turnover m-DNA and insoluble proteins may constitute a major unit. 9. The mitochondrial protein contents of the three tissues are not affected by thyroidectomy. 10. No correlation was seen between the turnover rate of mitochondria and cathepsin activity in any of the tissues under study in normal or thyroidectomized animals. 11. On the other hand, mitochondrial proteinase activity shows good correlation with the turnover rates of mitochondria in normal animals, and a parallel decrease in activity comparable with the decreased rates of turnover is observed after thyroidectomy. 12. It is concluded that mitochondrial proteinase activity may play a significant role in their protein turnover.

Animals↗

PubMed1979

Macrophage protein turnover. Evidence for lysosomal participation in basal proteolysis.

1. Turnover of intracellular proteins in cultured mouse macrophages was found to be slightly accelerated by the omission of serum from the culture medium. Media containing 10% (v/v) or more of serum established basal degradation rates in the cultures. 2. Basal degradation rates varied considerably between experiments, probably as a result of variable activation in vivo of the macrophages. 3. The selective carboxyl proteinase inhibitor pepstatin, which appeared to enter the lysosomes of the cells by pinocytosis, gave a progressive inhibition of basal proteolysis up to a maximum of about 40%. Cellular cathepsin D was largely inhibited after 48h of cultivation with pepstatin (100 micrograms/ml). 4. Leupeptin and 7-amino-1-chloro-3-tosylamidoheptan-2-one are less selective proteinase inhibitors. They also induced 25--35% inhibition of degradation, but their actions may not have been restricted to lysosomes. 5. Several solutes and particles that are endocytosed by macrophages and stored in lysosomes induce some inhibition of basal proteolysis, whether or not they themselves are substrates for proteolysis. 6. Colchicine was without effect on protein degradation, but cytochalasin B and the local anesthetics lidocaine and procaine, all of which have effects on microfilaments, were significantly inhibitory. This inhibition may result from a decrease in the rate of autophagy, and thus of lysosomal proteolysis, due to prevention of microfilament action.

Animals↗

PubMed1977

Alterations of spore coat processing and protein turnover in a Bacillus cereus mutant with a defective postexponential intracellular protease.

A mutant with an alteration in the major intracellular serine protease produced by postexponential Bacillus cereus was isolated by screening mutants defective in spore germination. The purified enzyme from the mutant is more labile to heat and alkaline pH than the protease from the wild type. Protease activity appears at the same time as in the wild type but only reaches 50% of the specific activity and decays more rapidly during sporulation. Coincident with the decay is a decrease in the rate of protein turnover. Generation of amino acids by turnover seems to be important for sporulation because the number of spores produced by the mutant is increased 4- to 10-fold by addition of casamino acids. As anticipated, the mutant produces spores that germinate poorly but, surprisingly, these spores are very deficient in coat protein. Coat antigen is present in cell extracts of mutant and wild type, however, both as large molecules not found on mature spores and as spore coat protein monomers. The large molecules rapidly disappear in a pulse chase experiment in the wild type with some increase in the coat monomers. In mutant extracts, however, this large coat antigen is slowly and improperly processed.

Antigens, Bacterial↗

PubMed1977

Labile protein reserves and protein turnover.

The concept of a labile protein reserve is based on the relatively slow establishment of a new equilibrium in the rate of nitrogen excretion after an abrupt change in dietary supply. The evidence reviewed shows that a majority of this nitrogen is derived from or deposited in skeletal muscle proteins. The rates of synthesis and degradation of total body protein are rapid in large animals (man and swine) and are correlated with heat production. The rate of protein synthesis in skeletal muscle greatly exceeds the rate of growth and is sensitive to nutritional status. The rate exceeds the rate of degradation in response to the ingestion of an adequate diet so that tissue proteins are accumulated, but it decreases below the rate of degradation under conditions of deprivation. In this latter state, proteins of skeletal muscle supply amino acids for energy or for the synthesis of other more essential proteins, e.g., milk proteins during lactation. Thus, we conclude that the labile protein reserve is a product of the normal, dynamic metabolism of protein.

Animals↗

PubMed1979

Effect of metabolic conditions on protein turnover in yeast.

1. In yeast growing on ethanol a turnover rate of up to 2%/h was measured. As much as 80% of the protein was subject to turnover, and no marked heterogeneity in the rate of degradation of protein was observed. When the yeast grew on glucose, the protein was degraded at a lower rate (0.5-1%/h). 2. Starvation for a nitrogen source increased the rate of protein degradation severalfold, whereas deprivation of phosphate had only a marginal effect (30% increase). Removal of glucose from a medium containing 50mM-phosphate did not cause marked changes in the rate of protein degradation. In contrast, when the media were low in phosphate (0.1 mM) removal of glucose increased the rate of turnover 2-4-fold. 3. Protein degradation proceeded unimpaired when the intracellular concentration of ATP decreased from 4 to 1 mM, but stopped completely when it decreased below 0.3 mM.

Adenosine Triphosphate↗

PubMed1978

Ntau-methylhistidine (3-methylhistidine) and muscle protein turnover: an overview.

Actin and myosin, the contractile proteins of skeletal muscle, are methylated following peptide bond synthesis, with production of Ntau-methylhistidine (3-methylhistidine, 3-MeHis). During intracellular breakdown of these proteins, the 3-MeHis is released and excreted in the urine. Studies on tissue distribution of 3-MeHis and on its qunatitative excretion following administration to rats and to man show that urinary output of this amino acid provides a reliable index of the rate of myofibrillar protein breakdown in the musculature of intact rats and human subjects. Estimates of the fractional rate of muscle protein breakdown based on 3-MeHis data are consistent with rates computed by other techniques. By this technique, it has been shown that the fractional rate of muscle protein breakdown is not significantly different in the elderly as compared with young adults. However, since muscle mass is less in the elderly, it makes a smaller contribution to whole body protein breakdown with aging in humans. Output of 3-MeHis diminishes in growing rats and obese human subjects with protein or energy restriction, though the initial response of myofibrillar protein breakdown in growing rats to protein and protein-energy restriction differs. Measurement of 3-MeHis excretion has also proved useful in exploring the effects of physical and thermal trauma on the rate of muscle useful in exploring the effects of physical and thermal trauma on the rate of muscle protein breakdown.

Aging↗

PubMed1976

Effects of amyloid induction on plasma protein turnover, and its implication.

Using polyacrylamide gel electrophoresis and radioiodinated plasma proteins, data on the rate constant for synthesis and fractional degradation rates for albumin, alpha1-, alpha2-, beta-, and gamma-globulins were obtained during accelerated amyloid induction in a murine model. The results indicate that during amyloid induction there is an increased rate of synthesis of alpha2-, beta-, and gamma-globulins but only the alpha2-globulin degradation rate is accelerated. In this experimental system, should amyloid protein be a degradation product of a plasma fraction, the alpha2-globulin appears as the most likely precursor. The implications of our findings are discussed, and a new general mechanism of amyloid production is proposed.

Alpha-Globulins↗