Cell Wall Metabolism in Developing Strawberry Fruits

Cell wall metabolism was studied in strawberry receptacles (Fragariaananassa, Duchesne) of known age in relation to petal fall (PF).Polysaccharide and protein composition, incorporation of [¹⁴C]glucoseand [¹⁴C]proline by excised tissue, and the fate of ¹⁴CO₂ fixedby young, attached fruits were followed in relation to celldivision, cell expansion, fine structure, and ethylene synthesis. Cell division continued for about 7 d after PF although vacuolationof cells was already beginning at PF and the subsequent cellexpansion was logarithmic. There was an associated logarithmicincrease in sugar content per cell and a decreasing rate ofethylene production per unit fresh weight. During cell expansion radioactivity from [¹⁴C]glucose was incorporatedinto fractions identified as starch and soluble polyuronideand into glucose and galactose residues in the cell wall. Radioactivityfrom [¹⁴C]proline was also incorporated into the cell wall,but only 10 per cent of this activity was found in hydroxyproline.Correspondingly wall protein contained a low proportion of hydroxyprolineresidues. The proportion of radioactivity from ¹⁴CO₂ fixed byfruitlets remained constant in most sugar residues in the cellwall. The proportion of radioactivity in galactose fell, indicatingturnover of these residues. Between 21 and 28 d after PF receptacles became red and softenedbut there was no change in the rate of ethylene production.Cell expansion continued for at least 28 d. Tubular proliferationof the tonoplast and hydration of middle lamella and wall matrixmaterial had begun 7–14 d after PF but became extremeduring ripening. Associated with the hydration of the wall,over 70 per cent of the polyuronide in the wall became freelysoluble, and arabinose and galactose residues lost from thewall appeared in soluble fractions. There was no increase intotal polysaccharide during ripening and incorporation of [¹⁴C]glucoseinto polysaccharides ceased, although protein increased andincorporation of [¹⁴C]proline into wall protein continued.     

Influence of Etherel and Gibberellic Acid on Carbon Metabolism, Growth, and Essential Oil Accumulation in Spearmint (Mentha Spicata)

Changes in growth parameters and ¹⁴CO₂ and [U-¹⁴C]-sucrose incorporation into the primary metabolic pools and essential oil were investigated in leaves and stems of M. spicata treated with etherel and gibberellic acid (GA). Compared to the control, GA and etherel treatments induced significant phenotypic changes and a decrease in chlorophyll content, CO₂ exchange rate, and stomatal conductance. Treatment with etherel led to increased total incorporation of ¹⁴CO₂ into the leaves wheras total incorporation from ¹⁴C sucrose was decreased. When ¹⁴CO₂ was fed, the incorporation into the ethanol soluble fraction, sugars, organic acids, and essential oil was significantly higher in etherel treated leaves than in the control. However, [U-¹⁴C]-sucrose feeding led to decreased label incorporation in the ethanol-soluble fraction, sugars, organic acids, and essential oils compared to the control. When ¹⁴CO₂ was fed to GA treated leaves, label incorporation in ethanol-insoluble fraction, sugars, and oils was significantly higher than in the control. In contrast, when [U-¹⁴C]-sucrose was fed the incorporation in the ethanol soluble fraction, sugars, organic acids, and oil was significantly lower than in the control. Hence the hormone treatment induces a differential utilization of precursors for oil biosynthesis and accumulation and differences in partitioning of label between leaf and stem. Etherel and GA influence the partitioning of primary photosynthetic metabolites and thus modify plant growth and essential oil accumulation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of beta-D-xylosides on collagen synthesis in cultured fibroblasts.

Cultured normal human skin fibroblasts were incubated with [¹⁴C]proline in the presence and absence of 1.0 mM p-nitrophenyl-β-D-xylose. Formation of non-dialyzable hydroxyproline was used as a measure of collagen synthesis. Although total [¹⁴C]proline incorporation was similar in the two cultures, [¹⁴C]hydroxyproline formation was significantly decreased in the β-xyloside-treated cultures. Increasing the period of incubation increased the radioactivity of the insoluble collagen fraction in untreated fibroblasts, however, in β-xyloside-treated cultures no such increase was observed. In contrast to the decreased production of collagen, growth of cells in the presence of the β-xyloside induced the synthesis of high levels of soluble glycosaminoglycans as measured by ³⁵SO₄ incorporation into isolated polysaccharide.     

Properties of polygalacturonate and cell cohesion in apple fruit cortical tissue

Examination of the hydrodynamic properties of polygalacturonate fractions from unripe and ripe apple tissue suggested that the wall bound fraction was degraded during ripening but that the soluble fraction was not. Esterification of cell wall preparations with CH₂N₂ caused solubilisation of polygalacturonate. Acid MeOH caused more extensive solubilization, but this reagent hydrolysed arabinofuranosyl linkages. Both reagents reduced the cohesion of EtOH extracted apple tissue. This effect could also be achieved by treatment with sodium polyphosphate at pH 4 but not by EDTA or chaotropic agents. Free carboxyl groups on polygalacturonate probably maintain cell cohesion through co-operative binding of Ca²⁺ ions. The integrity of primary wall structure is thought to depend upon non-covalent bonding between cellulose, protein and polygalacturonate.     

Transition of Lipid Synthesis from Chloroplasts to a Cytoplasmic System during Hardening in Chlorella ellipsoidea

Chlorella ellipsoidea Gerneck (IAM C-27) was synchronously grown and cells at an intermediate stage in the ripening phase of the cell cycle were hardened at 3 C for 48 hours. At various times of hardening, the cells were pulse-labeled for 4 minutes with [¹⁴C]NaHCO₃ in the light or with [¹⁴C]glucose in the dark, and the incorporation rate of ¹⁴C into total lipids was determined. A high incorporation rate of [¹⁴C]NaHCO₃ at zero time of hardening decreased after 6 hours. In the next 15 hours, a distinct increase was noted. This increase occurred prior to the development of frost hardiness. Cycloheximide completely inhibited both the increase and the development, and 3-(3,4-dichlorophenyl)-1,1-dimethylurea remarkably lowered the high incorporation rate at zero time. The incorporation rate of [¹⁴C]glucose increased along with hardiness in the dark. These results suggest that the major site of lipid synthesis shifts from chloroplasts to a cytoplasmic system during hardening of Chlorella.     

Effect of experimental colchicine encephalopathy on brain protein synthesis and tubulin metabolism

Colchicine blocks axoplasmic flow and produces neurofibrillary degeneration. Brain slices from mice injected intracerebrally with colchicine incorporated more [¹⁴C]leucine into protein and had a decreased uptake of [¹⁴C]leucine into the perchloric acid-soluble pool than did their controls. Brain RNA content was decreased and free leucine increased by colchicine-induced encephalopathy. The specific activities of proteins from subcellular fractions of colchicine-injected brain were increased in the nuclear fraction, the 100,000-g supernatant, and its vinblastine-precipitable tubulin. The ratio of the specific activity of the crude mitochondrial fraction to that of the total homogenate was decreased, as would consistent with impaired movement of newly labeled protein into synaptosomes. Colchicine-injected brain extracts contained one or more cytosol fractions that stimulated ribosomal incorporation of [¹⁴C]leucine into protein in a cell-free system. Colchicine-binding-activity measurements indicated loss of soluble and particulate tubulin in colchicine-injected brains; the decrease of soluble tubulin was verified by its selective precipitation with vinblastine. Colchicine encephalopathy did not affect the rate of spontaneous breakdown of in vitro colchicine binding activity. Similarities of colchicine encephalopathy to the neuron's response to axonal damage suggest that colchicine-induced increase in protein synthesis may, in part, reflect a neuronal response to blockage of neuroplasmic transport.     

Effects of electroconvulsive shock and cycloheximide on the incorporation of amino acids into proteins of mouse brain subcellular fractions.

—The incorporation of [4,5-³H]lysine and [1-¹⁴C]leucine into the proteins of subcellular fractions of mouse brain was examined following a single electroconvulsive shock (ECS) or following cycloheximide injections. When the [³H]lysine was injected intraperitoneally immediately after the ECS the incorporation into total brain proteins was decreased by more than 50% as compared to sham controls. The proportion of lysine incorporated into the microsomal fraction was increased, but no changes were observed in the other subcellular fractions including the synaptosomal fraction. With extended pulses administered at various times after the ECS there was no change in total incorporation nor were selective effects seen in any subcellular fractions. With intracranial injections of both [³H]lysine and [¹⁴C]leucine the decreased incorporation caused by ECS was not observed, neither were there selective changes in any subcellular fraction. This lack of inhibition occurred because the intracranial injection itself severely inhibited [³H]lysine incorporation. Cycloheximide (30 mg/kg) which depressed [³H]lysine incorporation into brain proteins by 84% caused a selective depression of the incorporation into the cell-sap fraction and selective elevations into the microsomal and synaptosomal fractions. Similar changes were seen with a higher (amnestic) dose of cycloheximide (150 mg/kg) which inhibited incorporation by 94%. These data are interpreted in terms of the diverse mechanisms by which ECS and cycloheximide inhibit protein synthesis.     

Intermediary metabolism of carbon compounds by nitrifying bacteria

Summary The assimilation of¹⁴CO₂ and [2-¹⁴C] acetate, [3-¹⁴C] pyruvate, [5-¹⁴C] -ketoglutarate, [2,3-¹⁴C] succinate, [U-¹⁴C] glutamate and [U-¹⁴C] aspartate was followed in cell suspensions ofNitrosomonas europaea andNitrobacter agilis respectively. There was appreciable incorporation of these substrates even without adding the inorganic nitrogen compounds that are oxidized by these bacteria yielding ATP. In the soluble amino acid fraction most of¹⁴C label was recovered in glutamate while in the protein amino acids a more uniform distribution was found. Acetate was rapidly incorporated to a high level in both nitrifying bacteria while inNitrobacter there was a relatively lower uptake of the other substrates especially succinate. High levels of the NAD malate dehydrogenase and NADP isocitrate dehydrogenase were measured but no significant amounts of the other tricarboxylic acid cycle enzymes or NADH oxidase were found. Glutamate decarboxylase was detected in both organisms and the transferase assay for glutamine synthetase indicated a 30-fold higher activity for this enzyme inNitrobacter. The amino acid composition of the water soluble fraction was determined in both bacteria.     

Incorporation of UDPGlucose into Cell Wall Glucans and Lipids by Intact Cotton Fibers

The [¹⁴C] moiety from [³H]UDP[¹⁴C]glucose was incorporated by intact cotton fibers into hot water soluble, acetic-nitric reagent soluble and insoluble components, and chloroform-methanol soluble lipids; the [³H] UDP moiety was not incorporated. The ³H-label can be exchanged rapidly with unlabeled substrate in a chase experiment. The cell wall apparent free space of cotton fibers was in the order of 30 picomoles per milligram of dry fibers; 25 picomoles per milligram easily exchanged and about 5 picomoles per milligram more tightly adsorbed. At 50 micromolar UDPglucose, 70% of the [¹⁴C]glucose was found in the lipid fraction after both a short labeling period and chase. The percent of [¹⁴C]glucose incorporated into total glucan increased slightly with chase, but the fraction of total glucans incorporated into insoluble acetic-nitric reagent (cellulose) did increase within a 30-minute chase period. The data supports the concept that glucan synthesis, including cellulose, as well as the synthesis of steryl glucosides, acetylated steryl glucosides, and glucosyl-phosphoryl-polyprenol from externally supplied UDPglucose occurs at the plasma membrane-cell wall interface. The synthase enzymes for such synthesis must be part of this interfacial membrane system.     

A SOLUBLE PREPARATION FROM RAT BRAIN THAT INCORPORATES INTO ITS OWN PROTEINS [14C]ARGININE BY A RIBONUCLEASE-SENSITIVE SYSTEM AND [14C]TYROSINE BY A RIBONUCLEASE-INSENSITIVE SYSTEM

Abstract— A 100,000 g supernatant fraction from rat brain that was passed through a column of Sephadex G-25-40 was able, after addition of some factors, to incorporate [^I4C]arginine (apparent K_m= 5 μM) and [¹⁴C]tyrosine (apparent K_m= 20 μM) into its own proteins. The factors required for the incorporation of [¹⁴C]arginine were: ATP (optimal concentration = 0-25-2 μM) and Mg²⁺ (optimal concentration 5 mM). For the incorporation of [^I4C]tyrosine the required factors were: ATP (apparent K_m= 0-75 μM), Mg²⁺ (optimalconcentration 8-16 mM) and K⁺ (apparent K_m= 16 mM). Addition of 19 amino acids did not enhance these incorporations. Optimal pHs were: for [¹⁴C]arginine and [¹⁴C]tyrosine, respectively, 7-4 and 7-0 in phosphate buffer and 7–9 and 7-3-8-1 in tris-HCl buffer. Pancreatic ribonuclease abolished the incorporation of [¹⁴C]arginine but had practically no effect in the incorporation of [¹⁴C]tyrosine. Furthermore, [¹⁴C]arginyl-tRNA was a more effective donor of arginyl groups than [¹⁴C]arginine, whereas [¹⁴C]tyrosyl-tRNA was considerably less effective than [¹⁴C]tyrosine. The incorporations of [¹⁴C]arginine and [¹⁴C]tyrosine into brain proteins were from 25- to 2000-fold higher than for any other amino acid tested (12 in total). In brain [¹⁴C]arginine incorporation was higher than in liver and thyroid but somewhat lower than in kidney. In comparison to brain, the incorporation of [¹⁴C]tyrosine was negligible in liver, thyroid or kidney. Kinetic studies showed that the macromolecular factor in the brain preparation was complex. The protein nature of the products was inferred from their insolubilities in hot TCA and from the action of pronase that rendered them soluble. [¹⁴C]Arginine was bound so that its a-amino group remained free. Maximal incorporation of [¹⁴C]tyrosine in brain of 30-day-old rats was about one-third of that in the 5-day-old rat. The changes with postnatal age in the incorporation of [¹⁴C]arginine were not statistically significant.     

Some effects of aluminium on rat brain protein synthesis

1. Infant rats and rabbits received intraperitonal aluminium (Al) chloride (5, 10 or 20 mg Al/kg body weight) every third day from one to four weeks of age.2. When the polysomal fraction was tested in a protein synthesizing system, a significant increase in the incorporation of [¹⁴C] leucine, [¹⁴C] phenylalanine, or [³⁵S] methionine into proteins in vitro was observed at the higher doses in rats but not rabbits.3. The incorporation of [³⁵S]methionine into brain ferritin was measured using polysomal mRNA or mRNA “stored” in the ribonucleoprotein (RNP) particle fraction.4. The results suggest that Al exposure causes the mobilization of ferritin mRNA from the latter fraction to the polysomal fraction for increased ferritin synthesis.     

Metabolism of Labeled Exogenous Glucose in Fiber Flax Tissues

Labeled glucose solution was introduced into cut fiber flax plants (45–50 cm high) under a pressure of 0.1 bar for 30 min, 1, and 2 h using a special device. The highest quantities of labeled carbon were revealed in the woody tissue. Sucrose made up a considerable proportion in low molecular weight products of [2-¹⁴C]-glucose transformation (23.5%). Metabolism of labeled glucose in the leaves exposed to sunlight yielded a set of metabolites similar to products of ¹⁴CO₂ photoassimilation. In the shade, the pattern of ¹⁴C distribution in labeled compounds of the alcohol/water soluble fraction was similar to that in the light in mature leaves; while in juvenile leaves, ¹⁴C content decreased in sucrose and increased in organic and amino acids. In the shade, the incorporation of ¹⁴C into starch and hot water soluble polysaccharides increased at the expense of the acetone fraction (lipids and pigments), water/salt soluble proteins, and cellulose. Low light conditions increased the radioactivity ratio of sparingly soluble (KOH and Triton X-100 soluble) proteins to albumins and globulins. We propose that the synthesis of components of the photosynthetic apparatus in juvenile leaves is directly powered by photosynthesis and the photosynthesis of sucrose and the polymers compete for photosynthetic ATP. Appearance of sucrose in the xylem is due to its release from the phloem to the stem apoplast and the radial transfer to the xylem, where it is transported to the upper part of the shoot with the transpiration stream.__________Translated from Izvestiya Akademii Nauk, Seriya Biologicheskaya, No. 3, 2005, pp. 294–299.Original Russian Text Copyright © 2005 by Chikov, Avvakumova, Bakirova, Khamidullina.     

Purine reutilization in phytohemagglutinin-stimulated human T-lymphocytes.

Incubation of human peripheral blood T-lymphocytes with phytohemagglutinin (PHA) resulted in increased rates of metabolism of the purine bases adenine, hypoxanthine, and guanine. The respective rates decreased to unmeasurable levels in cells incubated without PHA. [¹⁴C]Adenine was converted predominantly into adenine nucleotides, with slight catabolism to hypoxanthine and very low conversion into guanine nucleotides. [¹⁴C]Guanine labeled predominantly the guanine nucleotide pool, but some adenine nucleotide formation also took place. From [¹⁴C]hypoxanthine, adenine nucleotides in the soluble pool were more heavily labeled than the guanine nucleotides, whereas in the nucleic acid fraction the latter contained more radioactivity. Adenosine at low concentrations was mainly phosphorylated to adenine nucleotides, but at higher concentrations this process leveled off, while deamination continued to increase linearly. PHA-stimulation resulted in an increased rate of adenosine metabolism but no qualitative differences in comparison to unstimulated cells were observed. Enzyme assays indicated that after PHA-stimulation the activities of adenine and hypoxanthine phosphoribosyltransferases, and those of adenosine deaminase and kinase, increased with a peak at 48 h, when expressed on a per cell basis, but not at all when expressed per mg of protein. We conclude that stimulation of human T-lymphocytes with PHA increases the capacity of the cells for purine nucleotide synthesis from all the directly re-utilizable catabolic products, namely the purine bases and adenosine.     

Incorporation of radioactive glucosamine into macromolecules at nerve endings

Mice were injected intracerebrally with [¹⁴C]glucosamine, and incorporation into macromolecules in various subcellular fractions of brain was studied at a number of times after administration of the precursor. The [¹⁴C]glucosamine was rapidly incorporated into macromolecules of all the subcellular fractions of brain including both the soluble and particulate fractions of isolated nerve endings. Incorporation into macromolecules in the soluble fraction of nerve endings was quite extensive 3 hr after administration of the precursor and the specific acitvity of this fraction fell thereafter. In contrast there was only slight incorporation of [¹⁴C] leucine into the soluble protein from isolated nerve endings in the first few hours after administration, whereas the other subcellular fractions were maximally labelled at that time. The data suggests that, unlike protein which is largely transported to nerve endings in the axoplasm, there is extensive incorporation of carbohydrate into macromolecules in nerve endings. Whereas the protein component of a glycoprotein or mucopolysaccharide may be transported to the nerve ending from the perikaryon, the structure and function of this protein may be modified at the nerve ending by further incorporation of glucosamine, sialic acid and possibly other carbohydrates. The carbohydrate-containing macromolecules could influence nerve ending function immediately after these final synthetic reactions since these reactions occur at the nerve ending and not in the perikaryon.     

Lipid metabolism of ripening apples

Little change was observed in the concentration of sitosterol, the principal free sterol of apple, during ripening of the fruit in air at 12°. Phospholipid increased by ca 10% during the first 15–18 days and thereafter showed little change. Phosphatidylcholine increased during ripening whilst phosphatidylethanolamine exhibited a transitory increase in the first 7–18 days. Incorporation of [¹⁴C]acetate into free sterol by apple cortical discs showed little change during ripening but incorporation into phospholipids increased substantially between days 1 and 15 with a 27-fold increase in incorporation into phosphatidylcholine and an 8-fold increase into phosphatidylethanolamine and phosphatidylinositol.     

Distribution and metabolism of arachidonic and docosahexaenoic acids in rat pineal cells. Effect of norepinephrine

The time-course incorporation of 10 μM [¹⁴C]arachidonic (AA) and docosahexaenoic (DHA) acids into glycerolipids was studied in rat pineal cells. The incorporation of both labeled fatty acids into total lipids was approximately equal, but their distribution profiles among the various cell lipids showed marked differences. The esterification of [¹⁴C]DHA in the neutral lipids, triacylglycerols (TAG) and cholesterol esters (CE), was 2-fold higher than that of [¹⁴C]AA whereas the opposite could be observed in total phospholipids (PL). The order of incorporation into PL was phosphatidylcholine (PC) > phosphatidylinositol (PI) = phosphatidylethanolamine (PE) for [¹⁴C]AA and PC = PE for [¹⁴C]DHA, the incorporation of both fatty acids being not detected in phosphatidylserine (PS) and that of DHA not in PI. When using 0.5 μM [³H] fatty acids, the respective distribution patterns resembled that of fatty acids at 10 μM, except for a lower proportion in TAG. The stimulation of ³H-labeled cells by 100 μM norepinephrine induced a 170% increase of basal release of [³H]AA into the medium, while [³H]DHA was virtually not released. However, the analysis of cell labeling revealed that both [³H] fatty acid levels were decreased in PL and increased in TAG. These findings suggest different involvement for AA and DHA in the pineal function. The preferential incorporation of DHA in TAG suggests that TAG might play an important role in the pineal enrichment with DHA. The absence of DHA release after NE stimulation, which however cannot be ascertained, may raise the question of the role of DHA in NE transduction.     

Alterations in the lipid content of pituitary gland and serum prolactin and growth hormone in cadmium treated rats

The present study was undertaken to assess whether chronic exposition to cadmium (Cd, 0.133 mM per liter for 2 months) through drinking water may affect the lipid contents in the pituitary anterior lobe (PAL) of adult male Wistar rats. As compared to metal non-exposed controls, PALs exposed to cadmium showed an increase in total phospholipid contents, which was associated to an increase of the incorporation of [1–¹⁴C]-methyl choline into phosphatidylcholine and of [U–¹⁴C]-glucose into total phospholipids. The incorporation of [1–¹⁴C]-methyl choline into sphingomyelin was not changed. Incorporation of [1–¹⁴C]-acetate into total fatty acids also increased but incorporation of [1–¹⁴C]-acetate into cholesterol did not change. The activity of phospholipase D decreased both in PALs from Cd exposed rats and in PAL dispersed cells treated with Cd in the culture medium from Cd non-exposed rats. In PALS from Cd exposed rats, a decrease of serum prolactin and growth hormone concentrations was determined. The results shown that cadmium modifies the lipid contents of pituitary gland and directly or indirectly the levels of prolactin and growth hormone in serum.     

Metabolism of phenylalanine and tyrosine in tobacco cell lines resistant and sensitive to p-fluorophenylalanine

Chromatography of soluble polyphenols of p-fluorophenylalanine-sensitive and -resistant tobacco cells revealed that the 10-fold increased level found in the resistant line was largely due to the accumulation of two unidentified polyphenols. The uptake of Phe-[U-¹⁴C] and Tyr-[U-¹⁴C] by the resistant line was ca 10 % that by the sensitive line. About 90 % of the phenylalanine-[¹⁴C] which was taken up by both cell lines could be accounted for as free phenylalanine in protein, soluble polyphenols or CO₂. The fate of Tyr-[¹⁴C] was similar to that of phenylalanine except that the incorporation was into insoluble polymeric forms of polyphenols rather than into soluble polyphenols. The resistant line incorporated 9-times more phenylalanine-[¹⁴C] into soluble polyphenols than did the sensitive line. The different ¹⁴C-aromatic amino acid accumulation and incorporation patterns noted with the two cell lines indicates that there are different active pools. Differential uptake rates by the two cell lines might affect the distribution of the absorbed amino acid among the different pools.     

INCORPORATION OF [14C]N-ACETYL NEURAMINIC ACID INTO BRAIN GLYCOPROTEINS AND GANGLIOSIDES IN VIVO1

—Intracerebrally administered [¹⁴C]N-acetyl neuraminic acid was incorporated into brain glycoproteins and gangliosides. Incorporation into both classes of compounds was markedly inhibited by acetoxycycloheximide but incorporation into the soluble glycoproteins of the nerve-ending fraction was inhibited least of all. In contrast to glucosamine and fucose, a relatively small proportion of the injected [¹⁴C]NANA was incorporated.     

Changes in protein synthesis in rats in response to endurance training

Experiments were conducted to investigate the influence of endurance exercise training on protein synthesis in skeletal muscle, heart, and liver. Training decreased incorporation of [¹⁴C]-leucine into proteins of the stromal fraction of muscle but there was no change in amino acid incorporation into proteins of the sarcoplasmic and myofibrillar fractions. Incorporation of [¹⁴C]-leucine into the protein of heart, liver, and plasma was depressed in trained rats compared to untrained rats. The specific radioactivity of [¹⁴C]-leucine was similar in tissues of trained and untrained rats and thus the depressed amino acid incorporation represents a decrease in the rate of protein synthesis. These observations demonstrate that the adaptation of muscle protein metabolism to endurance training is quite different than the alterations during work-induced hypertrophy of muscle. The difference in adaptation probably relates to the functional differences between the types of exercise. However depression of protein synthesis in trained rats is a general effect in several tissues and not an effect localized in muscle tissue.