Protein synthesis during hypoxia in fetal lambs

1987 ◽  
Vol 252 (4) ◽  
pp. E519-E524 ◽  
Author(s):  
J. R. Milley
Keyword(s):  
Protein Synthesis ◽  
Oxygen Consumption ◽  
Steady State ◽  
Oxygen Concentration ◽  
Oxygen Delivery ◽  
Specific Activity ◽  
Fetal Hypoxia ◽  
Tyrosine Uptake ◽  
Inspired Oxygen ◽  
Plasma Compartment

The goal of this study was to test the hypothesis that the rate of fetal protein synthesis decreases during fetal hypoxia. Catheters were inserted into 13 sheep fetuses under maternal spinal and local fetal anesthesia. Five days after surgery, an infusion of L-[1-14C]tyrosine (0.05-0.25 muCi/min) was begun. Measurements were first made when tyrosine-specific activity reached steady state at 3 h and then again 3 h after fetal oxygen delivery was reduced by lowering the maternal inspired oxygen concentration. Fetal tyrosine uptake across the umbilical circulation was 1.34 +/- 0.20 mumol X kg-1 X min-1 during normoxia and decreased to 0.72 +/- 0.12 mumol X kg-1 X min-1 during hypoxia (P = 0.017). Tyrosine use from the plasma compartment was 1.25 +/- 0.18 mumol X kg-1 X min-1 during normoxia and decreased to 0.64 +/- 0.12 mumol X kg-1 X min-1 (P = 0.0005) during hypoxia. Fetal tyrosine use decreased during reduced oxygen delivery because the rate of tyrosine use for fetal protein synthesis decreased from 0.97 +/- 0.17 to 0.38 +/- 0.09 mumol X kg-1 X min-1 (P = 0.0004). Fetal oxygen consumption decreased by 40 mumol X kg-1 X min-1 during hypoxia. Decreased protein synthesis reduced the energy needed for protein synthesis and explained 28 mumol X kg-1 X min-1 of this reduction.

Role of glucose in corneal metabolism

1985 ◽  
Vol 249 (5) ◽  
pp. C409-C416 ◽  
Author(s):  
R. S. Thies ◽  
L. J. Mandel
Keyword(s):  
Oxygen Consumption ◽  
Steady State ◽  
Specific Activity ◽  
Krebs Cycle ◽  
Lactate Production ◽  
Minor Component ◽  
Acid Oxidation ◽  
Endogenous Fatty Acid ◽  
Nonsteady State ◽  
A Minor

Glucose catabolism by glycolysis and the Krebs cycle was examined in the isolated rabbit cornea incubated with [6-14C]glucose. The production of [14C]lactate and 14CO2 from this substrate provided minimal values for the fluxes through these pathways since the tissue was in metabolic steady state but not isotopic steady state during the 40-min incubation. The specific activity of lactate under these conditions was one-third of that for [6-14C]glucose, and label dilution by exchange with unlabeled alanine was minimal, suggesting that glycogen degradation was primarily responsible for this dilution of label in the Embden-Meyerhof pathway. In addition, considerable label accumulation was found in glutamate and aspartate. Calculations revealed that these endogenous amino acid pools were not isotopically equilibrated after the incubation period, suggesting that they were responsible for the isotopic nonsteady state by exchange dilution through transaminase reactions with labeled intermediates. An estimate of glucose oxidation by the Krebs cycle, which was corrected for label dilution by exchange, indicated that glucose could account for most of the measured corneal oxygen consumption that was coupled to oxidative phosphorylation. A minor component of this respiration could not be accounted for by glucose or glycogen oxidation. Additional experiments suggested that endogenous fatty acid oxidation was probably also active under these conditions. Finally, reciprocal changes in plasma membrane Na+-K+-ATPase activity induced by ouabain and nystatin were found to concomitantly alter oxygen consumption rates and [14C]lactate production from [6-14C]glucose. These results demonstrated the capacity for regulating glycolysis and the Krebs cycle in response to changing energy demands in the cornea.

Measurement in vivo of rumen microbial protein synthesis

1975 ◽  
Vol 26 (4) ◽  
pp. 689 ◽  
Author(s):  
DJ Walker ◽  
CJ Nader
Keyword(s):  
Protein Synthesis ◽  
Steady State ◽  
Flow Rate ◽  
Crude Protein ◽  
Specific Activity ◽  
Microbial Protein ◽  
Microbial Protein Synthesis ◽  
Microbial Nitrogen ◽  
Inorganic Sulphate

A method is described for the measurement in vivo of ruminal microbial protein synthesis. The method depends upon the incorporation into microbial protein of sulphur derived from 35S -labelled inorganic sulphate infused continuously into the rumen. Steady-state labelling of rumen digesta protein and specific activity of microbial sulphur are used, along with estimates of total digesta mass, to calculate total microbial sulphur in the rumen. The rate of disappearance of isotope from the rumen after cessation of [35S]sulphate infusion is used to calculate the flow rate of microbial s~dphur from that organ. Microbial sulphur may be used to estimate microbial nitrogen or crude protein by means of conversion factors.

A novel open-system technique to monitor real-time oxygen consumption during early phases of seed germination

2004 ◽  
Vol 14 (1) ◽  
pp. 17-26 ◽  
Author(s):  
C. Jacyn Baker ◽  
Daniel P. Roberts ◽  
Norton M. Mock ◽  
Vansie L. Blount
Keyword(s):  
Oxygen Consumption ◽  
Steady State ◽  
Seed Germination ◽  
Real Time ◽  
Oxygen Concentration ◽  
Open System ◽  
Aqueous Environment ◽  
Bathing Solution ◽  
Closed Chamber

A novel technique allows long-term monitoring of real-time oxygen consumption during seed germination in an open system. Most current techniques used to detect oxygen consumption by seeds measure the decrease in oxygen concentration in a closed chamber. This is not ideal for long-term experiments because the chamber must be replenished with air periodically, subjecting the seeds to abrupt changes in oxygen concentration. The current technique employs an open system, in which seeds are submerged in a continuously aerated aqueous environment. Oxygen electrodes are used to measure the steady-state concentration of oxygen in the solution, which is a function of both the rate of oxygen consumption by the seed and the rate of aeration from the atmosphere. The rate of aeration is directly dependent on the oxygen concentration of the bathing solution; therefore, previous calibration of the system allows the direct conversion of steady-state oxygen concentrations into oxygen consumption rates. Because oxygen is not limiting, the experimental design described here can monitor the same sample non-intrusively every minute for more than 24 h, allowing for greater precision than hourly readings often reported with current techniques. Multiple treatments and/or replicates can be run simultaneously, allowing sensitive comparison of various seed treatments or seed types. To illustrate its potential application, the technique was used to follow the rehydration and pre-emergence phases of germination of cucumber (Cucumis sativum), pea (Pisum sativum) and mustard (Brassica juncea) seeds, detect the inhibitory effects of surface sterilization techniques on seed respiration of cucumber, and follow the interaction of a bacterial biocontrol agent with germinating cucumber and pea seeds.

Influence of valine flooding on channeling of valine into tissue pools and on protein synthesis

1995 ◽  
Vol 268 (4) ◽  
pp. E735-E744 ◽  
Author(s):  
C. B. Smith ◽  
Y. Sun
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Steady State ◽  
Correction Factor ◽  
Specific Activity ◽  
Tissue Protein ◽  
Precursor Pool ◽  
Arterial Plasma ◽  
State Breakdown

Rates of valine incorporation into protein were measured under control and valine-"flooding" conditions and included correction for the degree of recycling of unlabeled valine derived from the steady-state breakdown of tissue protein into the precursor pool (tRNA bound). The correction factor lambda, which is the ratio of the steady-state specific activity of valine in the tissue tRNA-bound pool to that in the arterial plasma, was determined for each of the tissues. In controls, values of lambda ranged from 0.31 in adrenals to 0.54 in heart; in flooded animals, values were higher, but only in liver was the value of lambda close to 1.0. In control and flooded rats, rates of protein synthesis were highest in liver and adrenals and lowest in skeletal muscle, with intermediate values in brain and heart. Flooding resulted in increased rates of protein synthesis in liver and decreased rates in adrenals. Rates of protein synthesis in brain, heart, and skeletal muscle were not statistically significantly affected by flooding.

Rates of protein synthesis and turnover in fetal life

1981 ◽  
Vol 240 (3) ◽  
pp. E320-E324 ◽  
Author(s):  
P. R. Meier ◽  
R. G. Peterson ◽  
D. R. Bonds ◽  
G. Meschia ◽  
F. C. Battaglia
Keyword(s):  
Protein Synthesis ◽  
Steady State ◽  
Specific Activity ◽  
Large Fraction ◽  
Vena Cava ◽  
Total Content ◽  
Fetal Life ◽  
Fetal Plasma ◽  
Fractional Rate ◽  
Ovine Fetus

Uniformly labeled [14C]lysine was infused at constant rate into the inferior vena cava of eight ovine fetuses with gestational ages ranging from 110 to 145 days. The infusion lasted 9 to 13 h and produced a steady-state specific activity of free lysine in the fetal plasma. In the steady state, approximately 9% of the infused radioactivity was excreted by the fetus as 14CO2, indicating fetal catabolism of lysine. At the end of the infusion, the fetal carcass was analyzed for its total content of labeled and unlabeled lysine. The rate of protein synthesis was calculated from the carcass-to-plasma lysine specific activity ratio. The fractional rate constant (Ks) for the unidirectional flux of lysine into fetal proteins was inversely related (r = -0.88) to fetal age: Ks = 0.584 - 0.0036 age (days). In each fetus, Ks was 2-4 times greater than the estimated fractional rate of fetal protein accretion (KG). The discrepancy between Ks and KG demonstrates that a large fraction of protein synthesis in the ovine fetus is devoted to protein turnover.

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