A role for leucine in regulation of protein turnover in working rat hearts

1980 ◽  
Vol 239 (6) ◽  
pp. E510-E514 ◽  
Author(s):  
B. H. Chua ◽  
D. L. Siehl ◽  
H. E. Morgan
Keyword(s):  
Protein Synthesis ◽  
Protein Degradation ◽  
Nitrogen Balance ◽  
Plasma Levels ◽  
Protein Turnover ◽  
Ribosomal Subunits ◽  
Rat Hearts ◽  
Plasma Leucine ◽  
Beta Hydroxybutyrate

Effect of leucine on protein turnover was examined in perfused hearts provided with 1 (0.2 mM) or 5 times (1 mM) plasma levels of leucine and normal plasma levels of other amino acids. When hearts were perfused as Langendorff or working preparations with buffer that contained 15 mM glucose, protein degradation was 2–3 times faster than protein synthesis. As a result, the heart was in marked negative nitrogen balance. Addition of 1 mM leucine significantly improved the nitrogen balance (24–33%) by stimulating protein synthesis in Langendorff preparations (25%) and inhibiting protein degradation in both preparations (14–29%). The stimulatory effect of leucine on protein synthesis was associated with a reduction in levels of ribosomal subunits. In hearts supplied physiological levels of glucose, lactate, beta-hydroxybutyrate, insulin, and glucagon, protein synthesis was more nearly equal to protein degradation. Provision of 1 mM leucine stimulated protein synthesis only in Langendorff preparations (32%) but did not have a significant effect on protein degradation in either preparation. Although leucine did not have a significant effect on either protein synthesis or degradation in working hearts, nitrogen balance became positive with addition of 1 mM leucine. These results suggest that leucine may exert an effect on myocardial nitrogen balance in vivo under conditions that elevate plasma leucine concentrations.

Changes in protein turnover in rat uterus during pregnancy

1986 ◽  
Vol 250 (2) ◽  
pp. E114-E120 ◽  
Author(s):  
A. J. Morton ◽  
D. F. Goldspink
Keyword(s):  
Protein Synthesis ◽  
Protein Degradation ◽  
Protein Turnover ◽  
Cathepsin D ◽  
Cell Loss ◽  
Protein Breakdown ◽  
Rat Uterus ◽  
Fractional Rate ◽  
Uterine Growth

The adaptive growth and protein turnover of the rat uterus were studied during the 21 days of gestation and up to 3 days after parturition. Despite large increases (13-fold) in uterine size during gestation, the fractional rate of protein synthesis (measured in vivo) remained unchanged when compared with nonpregnant tissue values of 44 +/- 5%/day. However, decreases were found in the rate of protein breakdown after implantation (i.e., 75% on day 7 and 28% on day 11) and in the activity of cathepsin D (i.e., 33 and 85% on days 8 and 16 of gestation). Changes in the degradative processes would therefore appear to be primarily responsible for the massive uterine growth during pregnancy. In contrast to the uterus the fractional rates of synthesis in the placenta and fetus progressively decreased during gestation. After parturition the uterus rapidly returned to its normal size by a combination of cellular atrophy and cell loss. After 2 days, a complementary decrease in the fractional rate of synthesis (30%) and an increase in protein degradation (2-fold) explained the process of involution.

scholarly journals Rates of protein turnover in vivo and in vitro in ventricular muscle of hearts from fed and starved rats

1984 ◽  
Vol 222 (2) ◽  
pp. 395-400 ◽  
Author(s):  
V R Preedy ◽  
D M Smith ◽  
N F Kearney ◽  
P H Sugden
Keyword(s):  
Protein Synthesis ◽  
Protein Degradation ◽  
Protein Turnover ◽  
Synthesis Rate ◽  
Protein Synthesis Rate ◽  
Ventricular Muscle ◽  
Degradation Rates ◽  
Perfused Hearts

Starvation of 300 g rats for 3 days decreased ventricular-muscle total protein content and total RNA content by 15 and 22% respectively. Loss of body weight was about 15%. In glucose-perfused working rat hearts in vitro, 3 days of starvation inhibited rates of protein synthesis in ventricles by about 40-50% compared with fed controls. Although the RNA/protein ratio was decreased by about 10%, the major effect of starvation was to decrease the efficiency of protein synthesis (rate of protein synthesis relative to RNA). Insulin stimulated protein synthesis in ventricles of perfused hearts from fed rats by increasing the efficiency of protein synthesis. In vivo, protein-synthesis rates and efficiencies in ventricles from 3-day-starved rats were decreased by about 40% compared with fed controls. Protein-synthesis rates and efficiencies in ventricles from fed rats in vivo were similar to values in vitro when insulin was present in perfusates. In vivo, starvation increased the rate of protein degradation, but decreased it in the glucose-perfused heart in vitro. This contradiction can be rationalized when the effects of insulin are considered. Rates of protein degradation are similar in hearts of fed animals in vivo and in glucose/insulin-perfused hearts. Degradation rates are similar in hearts of starved animals in vivo and in hearts perfused with glucose alone. We conclude that the rates of protein turnover in the anterogradely perfused rat heart in vitro closely approximate to the rates in vivo in absolute terms, and that the effects of starvation in vivo are mirrored in vitro.

scholarly journals Effect of corticosterone treatment on muscle protein turnover in adrenalectomized rats and diabetic rats maintained on insulin

1982 ◽  
Vol 204 (3) ◽  
pp. 663-672 ◽  
Author(s):  
Bhanu R. Odedra ◽  
David J. Millward
Keyword(s):  
Protein Synthesis ◽  
Protein Degradation ◽  
Protein Turnover ◽  
Muscle Wasting ◽  
Muscle Protein ◽  
Diabetic Rats ◽  
Constant Infusion ◽  
Degradation Rates ◽  
Adrenalectomized Rats

The effect of corticosterone on protein turnover in skeletal muscle was investigated in growing rats. Protein synthesis was measured in vivo by the constant infusion of [14C]tyrosine. The extent to which any effect of corticosterone is modulated by the hyperinsulinaemia induced by steroid treatment was examined by giving the hormone not only to adrenalectomized rats but also to streptozotocin-induced diabetic rats maintained throughout the treatment period on two dosages of insulin by an implanted osmotic minipump. Approximate rates of protein degradation were also estimated in some cases as the difference between synthesis and net change in muscle protein mass. Measurements were also made of free 3-methylhistidine concentration in muscle and plasma. At 10mg of corticosterone/100g body wt. per day, growth stopped and muscle wasting occurred, whereas at 5 mg of corticosterone/100g body wt. per day no net loss of protein occurred. However, this low dose did induce muscle wasting when insulin concentration was regulated by a dose of 1.2 units/day. Protein synthesis was markedly depressed in all treated groups, the depression in the insulin-maintained rats being marginally more than in the hyperinsulinaemic adrenalectomized rats. The oxidative soleus muscle appeared to be less susceptible to the effect of the corticosterone than was the more glycolytic plantaris or gastrocnemius muscle. Any effect of the corticosterone on protein degradation was much less than its effects on protein synthesis. Where increases in the degradation rates appeared to occur in the rats treated with 10mg of corticosterone/100g body wt. per day, the increases were less than 20%. The free intracellular 3-methylhistidine concentrations were doubled in all groups treated with 5 mg of corticosterone/100g body wt. per day and increased 5-fold in the adrenalectomized rats treated with 10mg of corticosterone/100g body wt. per day, with no change in plasma concentration in any of the groups. It is therefore concluded that: (a) the suppression of protein synthesis is the main effect of glucocorticoids in muscle; (b) marked increases in insulin afford only minor protection against this effect; (c) stimulation of protein degradation may occur, but to a much lesser extent.

Regulation of protein synthesis and degradation during in vitro cardiac work

1980 ◽  
Vol 238 (5) ◽  
pp. E431-E442 ◽  
Author(s):  
H. E. Morgan ◽  
B. H. Chua ◽  
E. O. Fuller ◽  
D. Siehl
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Protein Degradation ◽  
Nitrogen Balance ◽  
Cardiac Work ◽  
Amino Acid Availability ◽  
Intracellular Concentrations ◽  
Substrate Mixtures ◽  
Beta Hydroxybutyrate

Cardiac work increased protein synthesis in hearts supplied glucose (mixture 1), glucose-insulin-glucagon-lactate-beta-hydroxybutyrate (mixture 2) or palmitate-beta-hydroxybutyrate-glucose (mixture 3). In hearts provided mixture 1, acceleration of synthesis involved increased rates of peptide chain initiation. In these hearts intracellular concentrations of 5 amino acids decreased and 13 others were unchanged, indicating that faster protein synthesis did not depend on increased amino acid availability. In hearts supplied mixtures 2, 3, or 4 (lactate-glucose-insulin), intracellular concentrations of branched-chain amino acids were decreased by work, whereas intracellular levels of some acidic and neutral amino acids increased. Protein degradation was decreased by work in hearts supplied mixtures 1 and 2, but not mixtures 3 and 4. In hearts provided mixture 1, nitrogen balance was negative, but less so in working preparations. Nitrogen balance was zero or positive in working hearts provided mixtures 2 and 4. These studies indicated that in hearts supplied some, but not all, of the substrate mixtures, cardiac work maintained efficiently of protein synthesis and inhibited protein degradation. An improved method for perfusion of working hearts with albumin-containing buffer is described.

Effects of diabetes on protein turnover in cardiac muscle

1980 ◽  
Vol 239 (3) ◽  
pp. E178-E185 ◽  
Author(s):  
I. H. Williams ◽  
B. H. Chua ◽  
R. H. Sahms ◽  
D. Siehl ◽  
H. E. Morgan
Keyword(s):  
Protein Synthesis ◽  
Protein Degradation ◽  
Protein Turnover ◽  
Isolated Heart ◽  
Chain Elongation ◽  
Cardiac Work ◽  
Ribosomal Subunits ◽  
Heart Muscle Cells ◽  
Whole Heart

Effects of alloxan diabetes of 10-day duration on protein turnover were investigated in hearts perfused with buffers simulating control and diabetic sera. Diabetes produced a 30% inhibition of protein synthesis in hearts perfused as Langendorff or working preparations. This reduction was attributable to a 20% fall in RNA concentration and a 10% decrease in efficiency of protein synthesis. Determination of RNA in ribosomal subunits indicated that the reduction in efficiency that was observed with diabetes may be due to an inhibition of polypeptide chain elongation/termination. Pharmacological levels of insulin (25 mU/ml) and cardiac work stimulated protein synthesis in both control and diabetic hearts. Effects of diabetes and insulin on protein synthesis in isolated heart muscle cells were similar to those found in whole heart. Diabetes increased protein degradation in hearts perfused with buffer similating diabetic serum and under conditions of cardiac work. Insulin (25 mU/ml) decreased protein degradation in both control and diabetic hearts. These studies indicate that long-term diabetes produces a greater negative nitrogen balance that, in contrast to control hearts, cannot be normalized by pharmacological levels of insulin or by cardiac work.

Respiratory energy requirements and rate of protein turnover in vivo determined by the use of an inhibitor of protein synthesis and a probe to assess its effect

1994 ◽  
Vol 92 (4) ◽  
pp. 585-594 ◽  
Author(s):  
T. J. Bouma ◽  
R. De Visser ◽  
J. H. J. A. Janssen ◽  
M. J. De Kock ◽  
P H. Van Leeuwen ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Protein Turnover ◽  
Energy Requirements ◽  
Inhibitor Of Protein Synthesis

scholarly journals LOCALIZED MUTAGENESIS FOR THE ISOLATION OF TEMPERATURE-SENSITIVE MUTANTS OF ESCHERICHIA COLI AFFECTED IN PROTEIN SYNTHESIS

Genetics ◽  
1979 ◽  
Vol 91 (2) ◽  
pp. 215-227
Author(s):  
W Scott Champney
Keyword(s):  
Escherichia Coli ◽  
Protein Synthesis ◽  
Temperature Sensitive ◽  
Chromosomal Locus ◽  
Ribosomal Subunits ◽  
Prolonged Incubation ◽  
Temperature Sensitive Mutants ◽  
Inhibition Of Growth ◽  
Localized Mutagenesis

ABSTRACT Two variations of the method of localized mutagenesis were used to introduce mutations into the 72 min region of the Escherichia coli chromosome. Twenty temperature-sensitive mutants, with linkage to markers in this region, have been examined. Each strain showed an inhibition of growth in liquid medium at 44°, and 19 of the mutants lost viability upon prolonged incubation at this temperature. A reduction in the rate of in vivo RNA and protein synthesis was observed for each mutant at 44°, relative to a control strain. Eleven of the mutants were altered in growth sensitivity or resistance to one or more of three ribosomal antibiotics. The incomplete assembly of ribosomal subunits was detected in nine strains grown at 44°. The characteristics of these mutants suggest that many of them are altered in genes for translational or transcriptional components, consistent with the clustering of these genes at this chromosomal locus.

Effect of glutamine-enriched total parenteral nutrition on septic rats

1991 ◽  
Vol 81 (2) ◽  
pp. 215-222 ◽  
Author(s):  
M. Salleh M. Ardawi
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Parenteral Nutrition ◽  
Protein Degradation ◽  
Total Parenteral Nutrition ◽  
Nitrogen Balance ◽  
Cumulative Percentage ◽  
Better Than

1. The effect of total parenteral nutrition with or without glutamine enrichment was studied in septic rats after 4 days of treatment. 2. Septic rats treated with glutamine-enriched total parenteral nutrition survived sepsis significantly better than other TPN-treated septic rats: the cumulative percentage of deaths over 4 days in septic rats treated with glutamine-enriched total parenteral nutrition was 25% compared with 55% in septic rats given total parenteral nutrition without glutamine and 70% in septic rats given glucose. 3. Glutamine-enriched total parenteral nutrition resulted in improved nitrogen balance in septic rats: the cumulative nitrogen balance over the 4 days of treatment was the least negative as compared with other groups of septic rats. 4. The rate of loss of intracellular glutamine in skeletal muscle was markedly decreased (P < 0.001) in response to glutamine-enriched total parenteral nutrition in septic rats. 5. The rate of protein synthesis was increased (21.2%) and the rate of protein degradation was decreased (35.5%) in response to glutamine-enriched total parenteral nutrition in septic rats. 6. It is concluded that the administration of glutamine-enriched total parenteral nutrition is beneficial to septic rats and possibly to septic patients.

Measurement of the Rate of Protein Synthesis in Muscle of Postabsorptive Young Men by Injection of a ‘Flooding Dose’ of [1-13C]leucine

1989 ◽  
Vol 77 (3) ◽  
pp. 329-336 ◽  
Author(s):  
Peter J. Garlick ◽  
Jan Wernerman ◽  
Margaret A. McNurlan ◽  
Pia Essen ◽  
Gerald E. Lobley ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Amino Acid ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Isotopic Enrichment ◽  
Plasma Leucine ◽  
Convenient Technique ◽  
Tissue Compartments ◽  
Muscle Biopsies

1. The ‘flooding dose’ technique for measuring the rate of protein synthesis in tissues in vivo involves the injection of a large amount of unlabelled amino acid together with the tracer to minimize differences in isotopic enrichment of the free amino acid in plasma and tissue compartments. This approach has been investigated in human muscle by taking biopsies from postabsorptive male volunteers given [1-13C]leucine. 2. Intravenous injection of 4 g of unlabelled leucine resulted in a rapid rise in free leucine concentration of seven- to eleven-fold in plasma and five-fold in muscle. Values were still elevated by two-fold after 2 h. 3. Five minutes after injection of [1-13C]leucine (0.05 g/kg) the isotopic enrichment of plasma leucine was 82% that of the injected material, falling to 44% at 120 min. The enrichment of free leucine in sequential muscle biopsies was close to that in plasma and almost identical to that for plasma α-ketoisocaproate. 4. The rate of protein synthesis was determined from the increase in leucine enrichment in protein of muscle biopsies taken before and 90 min after injection of [1-13C]leucine (0.05 g/kg; 19 or 39 atom% excess) and the average plasma α-ketoisocaproate enrichment over this period (taken to represent muscle free leucine). The mean rate of muscle protein synthesis in 10 subjects was 1.95 (sem 0.12)%/day. Rates of protein synthesis calculated from plasma leucine as precursor enrichment were only 5% lower than those calculated from plasma α-ketoisocaproate. 5. It is concluded that a ‘flooding dose’ of 13C-labelled amino acid is a useful and convenient technique for determining the rate of protein synthesis in tissues of human volunteers and patients.

scholarly journals The effect of protein depletion and repletion on muscle-protein turnover in the chick

1981 ◽  
Vol 194 (3) ◽  
pp. 811-819 ◽  
Author(s):  
M L MacDonald ◽  
R W Swick
Keyword(s):  
Protein Synthesis ◽  
Protein Turnover ◽  
Muscle Protein ◽  
Control Diet ◽  
Breast Muscle ◽  
Synthesis Rate ◽  
Protein Depletion ◽  
Protein Mass ◽  
Fractional Rate

Rates of growth and protein turnover in the breast muscle of young chicks were measured in order to assess the roles of protein synthesis and degradation in the regulation of muscle mass. Rates of protein synthesis were measured in vivo by injecting a massive dose of L-[1-14C]valine, and rates of protein degradation were estimated as the difference between the synthesis rate and the growth rate of muscle protein. In chicks fed on a control diet for up to 7 weeks of age, the fractional rate of synthesis decreased from 1 to 2 weeks of age and then changed insignificantly from 2 to 7 weeks of age, whereas DNA activity was constant for 1 to 7 weeks. When 4-week-old chicks were fed on a protein-free diet for 17 days, the total amount of breast-muscle protein synthesized and degraded per day and the amount of protein synthesized per unit of DNA decreased. Protein was lost owing to a greater decrease in the rate of protein synthesis, as a result of the loss of RNA and a lowered RNA activity. When depleted chicks were re-fed the control diet, rapid growth was achieved by a doubling of the fractional synthesis rate by 2 days. Initially, this was a result of increased RNA activity; by 5 days, the RNA/DNA ratio also increased. There was no evidence of a decrease in the fractional degradation rate during re-feeding. These results indicate that dietary-protein depletion and repletion cause changes in breast-muscle protein mass primarily through changes in the rate of protein synthesis.

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