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.

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.

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.

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.

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.

METABOLISM OF UNIFORMLY LABELLED MALTOSE-C14 INTRODUCED INTO DETACHED WHEAT AND TOBACCO LEAVES

1956 ◽  
Vol 34 (4) ◽  
pp. 569-576 ◽  
Author(s):  
G. Krotkov ◽  
S. Rizvi
Keyword(s):  
Paper Chromatography ◽  
Specific Activity ◽  
Starch Hydrolysis ◽  
Tobacco Leaves ◽  
Metabolic Pool ◽  
Wheat Leaves ◽  
Hydrolysis Of

Uniformly labelled C14-starch was incubated in the presence of saliva yielding radioactive maltose, which was isolated by paper chromatography. When this maltose was introduced into detached tobacco and wheat leaves, it was found to be respired and transformed into other carbohydrates. There was no evidence to indicate that maltose is either a better starch former than glucose or that it acts as a specific glucose donor to fructose in the synthesis of sucrose. No dilution in the specific activity of maltose was observed even under the conditions of starch hydrolysis. This indicates that hydrolysis of starch in vivo does not result in the addition of maltose to the metabolic pool of cells.

THE METABOLISM OF ASCARIS LUMBRICOIDES OVARIES: I. NITROGEN DISTRIBUTION

1955 ◽  
Vol 33 (1) ◽  
pp. 297-306 ◽  
Author(s):  
John K. Pollak ◽  
Donald Fairbairn
Keyword(s):  
Amino Acids ◽  
Ascaris Lumbricoides ◽  
Protein Fraction ◽  
Ammonia Nitrogen ◽  
High Concentration ◽  
Protein Nitrogen ◽  
Amino Amide ◽  
Protein Amino Acids ◽  
High Concentrations ◽  
Reducing Substances

The protein fraction obtained from Ascaris lumbricoides ovaries was analyzed for total, α-amino, and amide nitrogen, as well as amino acids and nucleic acids. In the corresponding non-protein fraction total, α-amino, amide, and ammonia nitrogen, and free amino acids and urea, were determined. Free and protein amino acids were qualitatively similar, but quantitatively dissimilar. Unusually large amounts of proline and alanine were found in the proteins, whereas arginine and methionine could not be identified in protein or free acids. Glutamic acid and alanine comprised one-half of the free acids. Ammonia was present in relatively high concentration, but urea was absent. Much of the non-protein nitrogen was not identified. Ribo- and desoxyribonucleic acids were found in approximately the relative proportions occurring in rat liver, but in much lower concentration. The existence of phosphoproteins was not clearly established. Glycogen and total reducing substances, however, were present initially in high concentrations which decreased markedly when the parasites were maintained in a non-nutrient medium.

THE PHYSIOLOGY OF HOST–PARASITE RELATIONS: VII. THE EFFECT OF STEM RUST ON THE NITROGEN AND AMINO ACIDS IN WHEAT LEAVES

1961 ◽  
Vol 39 (6) ◽  
pp. 1351-1372 ◽  
Author(s):  
Michael Shaw ◽  
Nicholas Colotelo
Keyword(s):  
Amino Acids ◽  
Stem Rust ◽  
Dry Weight ◽  
Aminobutyric Acid ◽  
Fresh Weight ◽  
Total N ◽  
Fourfold Increase ◽  
Barley Leaves ◽  
Protein Amino Acids ◽  
Wheat Leaves

The dry weight of leaf disks (2.8 mm in diameter) bearing pustules of stem rust and cut from primary leaves of Little Club wheat increased up to 2.5-fold, but the respective weights of host and parasite cannot be measured. By removal of the ectoparasitic mycelium of Erysiphe it was shown that approximately half of the increase in weight at infections of this organism on barley leaves was contributed by the fungus and half by the host.At infections of stem rust on Little Club there was a striking increase in total N per gram fresh weight and an increase in the ratio of soluble to insoluble N. Quantitative paper chromatographic analyses revealed a fourfold increase in free amino acids and nearly a twofold increase in protein amino acids per gram fresh weight by 9 days after inoculation. The most striking increases occurred in free glutamine, γ-aminobutyric acid, threonine, and those amino acids present only in trace amounts before inoculation, particularly the basic and aromatic acids. Only slight and transitory increases in N occurred at infections on Khapli and the infected leaves quickly reached a stage at which soluble and insoluble N and the ratios of soluble N to insoluble N and free to protein amino acids declined drastically. In Khapli, well-defined increases occurred in free glutamine and γ-aminobutyric acid. Particularly striking decreases occurred in glutamate, serine, threonine, glycine, and the leucines. The results are discussed.

scholarly journals The origin of nitrogen incorporated into compounds in the rumen bacteria of steers given protein- and urea-containing diets

1979 ◽  
Vol 41 (1) ◽  
pp. 197-209 ◽  
Author(s):  
D. N. Salter ◽  
K. Daneshvar ◽  
R. H. Smith
Keyword(s):  
Amino Acids ◽  
Rumen Fluid ◽  
Exchange Chromatography ◽  
The Other ◽  
Turnover Rates ◽  
Low Protein ◽  
Protein Amino Acids ◽  
Mixed Bacteria ◽  
N Enrichment ◽  
N Rates

1. Two young Friesian steers fitted with rumen cannulas were each given three different isonitrogenous and isoenergetic diets for successive periods of 2–3 weeks. The diets consisted mainly of straw and tapioca, with the nitrogen supplied mainly as decorticated groundnut meal (DCGM; diet A), in approximately equal amounts of DCGM and urea (diet B), or entirely as urea (diet C).2. At the end of each period on a given diet, part of the dietary urea of a morning feed was replaced by a solution of [15N]urea which was infused into the rumen. Samples of rumen contents were removed just before giving the15N dose and at 1, 3, 5, 7 and 24 h afterwards, concentrations of ammonia and its15N enrichment were determined and samples of mixed bacteria were prepared. Amino acids, ammonia derived mainly from amide groups, and hexosamines were prepared by ion-exchange chromatography of acid-hydrolysates of the bacteria and analysed for15N.3. Approximate estimates of net bacterial N synthesis were made from turnover data for rumen fluid and15N enrichments in rumen fractions. From the determined efficiency of incorporation of urea-N into bacteria recovered at the duodenum, it was calculated that on diets A, B and C respectively 82%, 37% and 0% of the bacterial N was derived from dietary protein or other non-urea sources.4. [15N]urea was converted rapidly to ammonia and the15N then incorporated into bacterial amide-N; it appeared at a slower rate in total bacterial non-amide-N. Rates of incorporation into non-amide-N were highest for glutamic acid, aspartic acid and alanine, and generally lowest for proline (pro), histidine (his), phenylalanine (phe), arginine (arg), methionine (met) and galactosamine. A similar ranking was also generally observed for relative15N abundances (15N atoms %excess in N component ÷15N atoms % excess in total bacterial N) achieved after several hours. Relative15N abundances in his, arg and pro increased with decreasing protein (DCGM) in the diet but those in the other protein amino acids, including the poorly labelled met phe (and its derivative tyrosine) did not.5. It was concluded that different extents of labelling of the amino acids (at least those present mainly in protein) indicated that different amounts of preformed units (amino acids or peptides) were used. When an adequate supply of such units was available (particularly on diet A) pro, arg, his, met and phe were derived in this way to a greater extent than the other amino acids, but whereas synthesis of pro, arg and his increased on the low-protein diet C, that of met and phe did not. Thus met and phe may be limiting for bacterial growth on diets low in protein and high in non-protein-N.6. Differences in the extent of labelling of other bacterial N components may be due to different turnover rates.

STUDIES ON WHEAT PLANTS USING CARBON-14 COMPOUNDS: XV. UTILIZATION OF SERINE-1-C14 AND SERINE-3-C14

1961 ◽  
Vol 39 (7) ◽  
pp. 1107-1111 ◽  
Author(s):  
W. B. McConnell ◽  
A. J. Finlayson
Keyword(s):  
Amino Acids ◽  
Specific Activity ◽  
Protein Fractions ◽  
Carbon 14 ◽  
Stages Of Growth ◽  
Protein Amino Acids ◽  
Late Stages ◽  
Carboxyl Carbon ◽  
Soluble Material ◽  
Preferential Incorporation

Thirty-five per cent and 43% of the carbon-14 from DL-serine-1-C14 and L-serine-3-C14, respectively, were found in the mature kernels of wheat plants to which the above tracers were administered by injection into the stem during late stages of growth. Total recoveries of carbon-14 in upper portions of the plant were 40% and 35% respectively. Radioactivity was extensively distributed among major kernel components with protein fractions having a somewhat greater specific activity than starch and ether-soluble material. Carbon-14 from both tracers was incorporated into all of the protein amino acids isolated, notable features being an extensive labelling of carboxyl carbon of glycine when DL-serine-1-C14 was used and preferential incorporation of serine carbon-3 into histidine. The results are in accord with the view that conversion of serine to glycine occurs largely by loss of serine carbon-3 and that little or no glycine is formed from serine via decarboxylation.

Measurement of protein turnover rates by heavy water labeling of nonessential amino acids

2006 ◽  
Vol 1760 (5) ◽  
pp. 730-744 ◽  
Author(s):  
R BUSCH ◽  
Y KIM ◽  
R NEESE ◽  
V SCHADESERIN ◽  
M COLLINS ◽  
...  
Keyword(s):  
Amino Acids ◽  
Heavy Water ◽  
Protein Turnover ◽  
Turnover Rates ◽  
Nonessential Amino Acids
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