PROTEIN METABOLISM AND RESPIRATION IN ATTACHED AND DETACHED PRIMARY WHEAT LEAVES

1964 ◽  
Vol 42 (4) ◽  
pp. 357-366 ◽  
Author(s):  
J. A. Hellebust ◽  
R. G. S. Bidwell
Keyword(s):  
Protein Metabolism ◽  
Protein Turnover ◽  
Soluble Sugars ◽  
Turnover Rates ◽  
Protein Amino Acid ◽  
Protein Nitrogen ◽  
Short Period ◽  
Detached Leaves ◽  
Amino Acid Turnover ◽  
Wheat Leaves

Attached and detached wheat leaves were supplied with C14O2 for a short period in light. They were then kept for 20 hours in the dark followed by 20 hours in light in air. Samples were taken at the beginning and end of each period and analyzed for protein nitrogen; and for amounts and total activities of respired carbon, soluble sugars, and amino acids and of protein amino acids.Similar patterns of protein metabolism were found in the two sets of leaves. The estimated protein amino acid turnover rates were somewhat higher in the detached than in the attached leaves but this may have been due to greater participation of soluble compounds which could not be translocated in detached leaves. There was a rapid synthesis of amides in the detached leaves during the light period, but this occurred at the expense of soluble sugars and supplied nitrogen salts rather than from protein breakdown products.Some contribution was made to respired CO2 by proteins during a period when protein turnover as well as a net decrease in proteins took place. During senescence, protein degradation contributed a considerable amount of carbon to respiration, but no protein turnover took place.

PROTEIN TURNOVER IN WHEAT AND SNAPDRAGON LEAVES: PRELIMINARY INVESTIGATIONS

1963 ◽  
Vol 41 (7) ◽  
pp. 969-983 ◽  
Author(s):  
J. A. Hellebust ◽  
R. G. S. Bidwell
Keyword(s):  
Amino Acids ◽  
Protein Turnover ◽  
Soluble Sugars ◽  
Turnover Rates ◽  
Time Intervals ◽  
Protein Nitrogen ◽  
Protein Amino Acids ◽  
Specific Activities ◽  
Wheat Leaves ◽  
Biochemical Differentiation

Detached primary wheat leaves and attached cotyledons and primary leaves of snapdragons were allowed to photoassimilate C14O2 for short periods of time. They were subsequently kept in air and samples were taken at various time intervals and analyzed for protein nitrogen, and amounts and total radioactivities of soluble sugars and amino acids and protein amino acids. A method of estimating protein turnover from these data is discussed. Amounts and specific activities of respired carbon were also determined for wheat leaves.Minimum protein turnover rates of about 0.5 to 1.5% per hour were found in rapidly growing snapdragon leaves and in snapdragon cotyledons. Lower rates were found in detached, non-growing wheat leaves and slowly growing snapdragon leaves. Little contribution could have been made by proteins as substrates for respiration in detached wheat leaves. It is suggested that protein turnover in leaves is mainly associated with growth and biochemical differentiation.

PROTEIN TURNOVER IN ATTACHED WHEAT AND TOBACCO LEAVES

1964 ◽  
Vol 42 (1) ◽  
pp. 1-12 ◽  
Author(s):  
J. A. Hellebust ◽  
R. G. S. Bidwell
Keyword(s):  
Amino Acids ◽  
Protein Turnover ◽  
Specific Activity ◽  
Soluble Sugars ◽  
Turnover Rates ◽  
Protein Nitrogen ◽  
Tobacco Leaves ◽  
Long Time ◽  
Protein Amino Acids ◽  
Wheat Leaves

Attached primary and secondary wheat leaves were supplied continuously with C14O2 during daily periods of photosynthesis for 3 days. Samples were analyzed for amounts and total activities of respired carbon, soluble sugars and amino acids, protein amino acids, and protein nitrogen. By labelling all possible protein precursors to the same extent it was possible to eliminate doubts about the specific activity of carbon entering protein. Hence turnover rates could be accurately established. Because tobacco leaves last for a long time, it was possible to label their proteins, wait until soluble compounds were at a low specific activity, and then measure turnover of proteins as radioactivity in them decreased.Protein amino acid turnover rates of 0.4–0.5% per hour were obtained in rapidly growing secondary wheat leaves and 0.2–0.3% per hour in non-growing primary wheat leaves. Turnover rates of 0.15–0.2% per hour were found in expanding tobacco leaves, but little or no turnover was found in fully expanded tobacco leaves.It is suggested that protein turnover is a facet of the biochemical differentiation that accompanies development, enlargement, or change in function of an organ without concomitant net protein synthesis.

SOURCES OF CARBON FOR THE SYNTHESIS OF PROTEIN AMINO ACIDS IN ATTACHED PHOTOSYNTHESIZING WHEAT LEAVES

1963 ◽  
Vol 41 (7) ◽  
pp. 985-994 ◽  
Author(s):  
J. A. Hellebust ◽  
R. G. S. Bidwell
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Glutamic Acid ◽  
Protein Turnover ◽  
Soluble Sugars ◽  
Protein Nitrogen ◽  
Considerable Portion ◽  
Protein Amino Acids ◽  
Specific Activities ◽  
Wheat Leaves

Attached, rapidly growing wheat leaves were allowed to photoassimilate C14O2 and C12O2 alternately. Samples of leaves were collected after each period of photosynthesis and were analyzed for amounts and total activities of soluble sugars and amino acids, and protein amino acids. The leaves were also analyzed for protein nitrogen and amounts and total activities of respired carbon. Samples of roots were also collected and the amounts, total activities, and specific activities of their soluble compounds were determined. It was possible to calculate from these data the proportions of carbon entering some protein amino acids which came either from soluble amino acid pools or by a direct route from photosynthate, bypassing the soluble pools. More than half of the carbon entering protein-bound serine and glycine was derived from newly assimilated CO2, while protein glutamic acid, aspartic acid, and alanine derived more of their carbon from the soluble amino acid pools. Analysis of the data from roots indicated that a considerable portion of the carbon translocated from the leaves was derived from newly assimilated CO2. There was some indication that protein turnover took place, but it was concluded that proteins could not have contributed significantly as substrates for respiration in these leaves.

A reappraisal of protein turnover values in neonates fed human milk or formula

1989 ◽  
Vol 67 (4) ◽  
pp. 282-286 ◽  
Author(s):  
P. B. Pencharz ◽  
R. Clarke ◽  
A. Papageorgiou ◽  
L. Farri
Keyword(s):  
Birth Weight ◽  
Human Milk ◽  
Nitrogen Metabolism ◽  
Protein Turnover ◽  
Nitrogen Isotopes ◽  
Nitrogen Excretion ◽  
Constant Infusion ◽  
Turnover Rates ◽  
Protein Nitrogen ◽  
Urea Nitrogen

We investigated the effect of human milk feeding on the nitrogen metabolism of appropriate-for-gestational age infants of birth weight 1.5–2.0 kg. Eight infants received pooled mature human milk. The remaining 20 were divided into two equal groups, who received one of two low-protein, milk-based formulae. The formulae were identical in composition except for the protein source, which was either casein- or whey-predominant. The three diet groups received similar total nitrogen (390 mg N∙kg−1∙d−1) and energy (500 kJ∙kg−1∙d−1) intakes. The human-milk-fed group, however, received a significantly higher intake of nonprotein and urea nitrogen and a significantly lower true protein nitrogen. Nitrogen metabolism was studied using a modified constant infusion of [15N]glycine, mixed with the feeding every 2–3 h. Urine was collected in approximately 3-h aliquots and analysed for total ammonia and urea nitrogen. Excretion of the 15N label was measured in urinary urea and ammonia. No differences were seen between the three diet groups in total [15N]urea or [15N]ammonia urinary excretion. However, the concentration of 15N in urinary urea in the human-milk-fed group was lower than in the two formula-fed groups. This reduction in concentration appeared due to a higher dietary intake of urea among the human-milk-fed group, and the consequent dilution of the label in the urine. As a result, protein turnover rates calculated from the [15N]urea end product were artificially raised in the milk-fed group, and were significantly higher than those in the formula groups. No differences were noted between the three diet groups in nitrogen turnover rates derived from the ammonia label. These rates averaged 61% of those derived from the urea end product. The two nitrogenous end products (ammonia and urea) appear to reflect different aspects of the neonates' nitrogen metabolism, in the form of pools or compartments that may be interchanging but are not always equilibrated.Key words: human milk, premature infant, low birth weight, nitrogen isotopes, protein metabolism.

A comparison of the estimates of whole-body protein turnover in parenterally fed neonates obtained using three different end products

1989 ◽  
Vol 67 (6) ◽  
pp. 624-628 ◽  
Author(s):  
P. Pencharz ◽  
J. Beesley ◽  
P. Sauer ◽  
J. Van Aerde ◽  
U. Canagarayar ◽  
...  
Keyword(s):  
Nitrogen Metabolism ◽  
Protein Metabolism ◽  
Protein Turnover ◽  
The Other ◽  
Whole Body ◽  
Turnover Rates ◽  
Body Protein ◽  
Future Studies ◽  
Simultaneous Measurements ◽  
End Products

Protein turnover rates in neonates have been calculated largely by measuring urinary [15N]urea enrichment following administration of [15N]glycine. Although ammonia has been increasingly recognized as an end product of nitrogen metabolism, in neonates it yields a different estimate of protein turnover than does urea. Comparisons of ammonia and urea end products in parenterally fed neonates have not previously been reported. A third and independent way of estimating protein turnover, developed for adults, is to use breath 13CO2 as an end product following administration of [1-3C]leucine. We therefore carried out simultaneous measurements of protein turnover in 10 parenterally fed neonates, using the three end products. The infants were clinically stable, weighed 2.6 ± 0.2 kg, and received 3.1 ± 0.2 g∙kg−1∙d−1 of amino acid, 2.2 ± 0.1 g∙kg−1∙d−1 of lipids, and an energy intake of 90 ± 4 kcal∙kg−1∙d−1 (1 kcal = 4.186 kJ). The turnover estimates derived from the 13CO2 and [15N]urea end products were very similar. The [15N]ammonia end product produced values approximately 66% (p < 0.01) of the other two. We conclude that the ammonia and urea end products probably originate in different precursor pools. The similarity of the urea and breath carbon dioxide results helps validate the use of the urea end product in studying the nitrogen metabolism of parenterally fed neonates. Ideally in future studies two or more end products should be used, since they provide information about different aspects of the nenonates' protein metabolism.Key words: neonates, protein metabolism, nitrogen-15, [1-13C]leucine.

scholarly journals Influence of Subcellular Localization and Functional State on Protein Turnover

Cells ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 1747
Author(s):  
Roya Yousefi ◽  
Kristina Jevdokimenko ◽  
Verena Kluever ◽  
David Pacheu-Grau ◽  
Eugenio F. Fornasiero
Keyword(s):  
Subcellular Localization ◽  
Functional State ◽  
Protein Turnover ◽  
Protein Localization ◽  
Small Gtpase ◽  
Turnover Rates ◽  
Cellular Behavior ◽  
Two Factors ◽  
Brain Creatine Kinase ◽  
Selection Of

Protein homeostasis is an equilibrium of paramount importance that maintains cellular performance by preserving an efficient proteome. This equilibrium avoids the accumulation of potentially toxic proteins, which could lead to cellular stress and death. While the regulators of proteostasis are the machineries controlling protein production, folding and degradation, several other factors can influence this process. Here, we have considered two factors influencing protein turnover: the subcellular localization of a protein and its functional state. For this purpose, we used an imaging approach based on the pulse-labeling of 17 representative SNAP-tag constructs for measuring protein lifetimes. With this approach, we obtained precise measurements of protein turnover rates in several subcellular compartments. We also tested a selection of mutants modulating the function of three extensively studied proteins, the Ca2+ sensor calmodulin, the small GTPase Rab5a and the brain creatine kinase (CKB). Finally, we followed up on the increased lifetime observed for the constitutively active Rab5a (Q79L), and we found that its stabilization correlates with enlarged endosomes and increased interaction with membranes. Overall, our data reveal that both changes in protein localization and functional state are key modulators of protein turnover, and protein lifetime fluctuations can be considered to infer changes in cellular behavior.

The Excretion of Isotope in Urea and Ammonia for Estimating Protein Turnover in Man with [15N]Glycine

1981 ◽  
Vol 61 (2) ◽  
pp. 217-228 ◽  
Author(s):  
E. B. Fern ◽  
P. J. Garlick ◽  
Margaret A. McNurlan ◽  
J. C. Waterlow
Keyword(s):  
Protein Metabolism ◽  
Protein Turnover ◽  
Mean Value ◽  
Intravenous Dose ◽  
Whole Body ◽  
Body Protein ◽  
End Products ◽  
The Mean ◽  
15N Urea ◽  
Normal Adults

1. Four normal adults were given [15N]-glycine in a single dose either orally or intravenously. Rates of whole-body protein turnover were estimated from the excretion of 15N in ammonia and in urea during the following 9 h. The rate derived from urea took account of the [15N]urea retained in body water. 2. In postabsorptive subjects the rates of protein synthesis given by ammonia were equal to those from urea, when the isotope was given orally, but lower when an intravenous dose was given. 3. In subjects receiving equal portions of food every 2 h rates of synthesis calculated from ammonia were much lower than those from urea whether an oral or intravenous isotope was given. Comparison of rates obtained during the post-absorptive and absorptive periods indicated regulation by food intake primarily of synthesis when measurements were made on urea, but regulation primarily of breakdown when measurements were made on ammonia. 4. These inconsistencies suggest that changes in protein metabolism might be assessed better by correlating results given by different end-products, and it is suggested that the mean value given by urea and ammonia will be useful for this purpose.

The role of NOS2 and NOS3 in renal protein and arginine metabolism during early endotoxemia in mice

2005 ◽  
Vol 288 (4) ◽  
pp. F816-F822 ◽  
Author(s):  
Yvette C. Luiking ◽  
Marcella M. Hallemeesch ◽  
Wouter H. Lamers ◽  
Nicolaas E. P. Deutz
Keyword(s):  
Blood Flow ◽  
Renal Blood Flow ◽  
Protein Turnover ◽  
De Novo ◽  
Whole Body ◽  
Wild Type ◽  
Protein Amino Acid ◽  
Renal Metabolism ◽  
Lps Challenge ◽  
Baseline Conditions

Previously, we observed an enhanced renal protein synthesis and increased de novo arginine production in the early response to endotoxemia in wild-type Swiss mice (Hallemeesch MM, Soeters PB, and Deutz NE. Am J Physiol Renal Physiol 282: F316–F323, 2002). To establish whether these changes are regulated by nitric oxide (NO) synthesized by NO synthase isoforms NOS2 and NOS3, we studied C57BL6/J wild-type (WT), NOS2-deficient (NOS2−/−), and NOS3-deficient (NOS3−/−) mice under baseline (unstimulated) and LPS-treated conditions. The metabolism of renal protein, amino acid, and arginine was studied at the whole body level and across the kidney by infusing the stable isotopes l-[phenyl-2H5]phenylalanine, l-[phenyl-2H2]tyrosine, l- guanidino-[15N2]arginine, and l-[ ureido-13C,2H2]citrulline. Renal blood flow was measured using radioactive PAH extraction. Under baseline conditions, renal blood flow was significantly reduced in NOS2−/− mice (0.29 ± 0.01 vs. 0.48 ± 0.07 ml·10 g body wt−1·min−1 in WT) ( P < 0.05), and de novo arginine production was lower in NOS2−/− mice. After LPS challenge, renal protein turnover and arginine production increased in all three groups ( P < 0.05), even though renal de novo arginine synthesis did not increase. The expected increase in renal citrulline production and disposal after LPS was not observed in NOS2−/− mice ( P = 0.06). Collectively, these data show that NOS2 is constitutively expressed in the kidney and remarkably functional as it affects renal blood flow and de novo arginine production under baseline conditions and is important for the increase in renal citrulline turnover during endotoxemia. NOS3, in contrast, appears less important for renal metabolism. The increase in renal protein turnover during endotoxemia does not depend on NOS2 or NOS3 activity.

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