Total Protein Amino Acid Research Articles

Research on cadmium toxicity mechanism during maize germination

为了深入探讨重金属胁迫下植物重金属代谢过程及机理, 采用有一定重金属镉耐受能力的农作物玉米为试验材料, 综合研究了不同镉浓度(5~100 μmol·L^-1)及不同处理时间下玉米幼苗发芽、不同组织部位镉含量及分布、镉中毒前后液相色谱 质谱联用谱图(HPLC-MS)、核磁共振氢谱图(1H NMR)和总蛋白氨基酸含量。结果表明, 低于50 μmol·L^-1的镉浓度能促进玉米发芽, 高于此浓度可明显抑制发芽。镉在胚乳、根、茎、芽等新鲜组织部位的分布不均, 其分布情况为: 胚乳>根>茎>芽。HPLC-MS和¹H NMR分析结果表明, 玉米中镉以金属螯合剂(PC)形式络合。总蛋白氨基酸含量分析说明镉胁迫影响营养物质的吸收及合成。重金属镉在整个玉米幼苗中传输积累过程为: 大量镉吸附在胚乳中, 部分直接吸附在根表面; 部分镉以游离形式存在, 部分以植物金属螯合剂螯合形式存在; 镉在细胞中与各种蛋白作用, 在胞液、液泡、胞间连丝等细胞器间传递; 镉经根、茎传输到芽, 此过程主要受浓度梯度影响; 镉的传输过程很可能遵循顺浓度梯度的协助扩散过程, 试验证明了此过程的合理性。

Isolation and analysis of natural compounds from silkworm pupae and effect of its extracts on alcohol detoxification

AbstractSilkworm pupae have much potential and many applications as a natural medicine to promote human health. However, their chemical components have not been fully characterized or understood. HPLC analysis was conducted to determine the content ratio (%) of individual amino acids in total protein of the pupae. It showed that glutamic acid (18.3%), histidine (14.6%) and alanine (10.2%) are the most common amino acids in silkworm pupae. Fatty acid composition of silkworm pupae oil was revealed by high‐pressure liquid chromatography and gas chromatography – mass spectroscopy analyses. They contain a high ratio of essential fatty acids, [α‐linolenic acid (ω‐3 fatty acid]+ linoleic acid) (49.0%), and also contain non‐essential fatty acids, oleic acid (19.9%), palmitoleic acid (2.5%), palmitic acid (19.7%), stearic acid (8.6%), and eicosapentaenoic acid (EPA) (0.3%). In addition, they also contain antioxidants, quercetin diglucoside and nutritionally important riboflavin (vitamin B2). This study suggests that silkworm pupae are a nutritionally valuable food product and are applicable as cosmetic components with essential amino acids, essential fatty acids, antioxidants and vitamins. The animal experiment showed that alcohol dehydrogenase (ADH) activity was significantly higher in the liver of mice orally administered with 0.5 mg/mL of silkworm extract and alcohol than with commercial Dawn808™ and alcohol, indicating that silkworm pupae extracts have alcohol detoxification activity.

Nutritional ecology of nominally herbivorous fishes on coral reefs

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 296:129-142 (2005) - doi:10.3354/meps296129 Nutritional ecology of nominally herbivorous fishes on coral reefs David J. Crossman1,*, J. Howard Choat2, Kendall D. Clements1 1School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand2Department of Marine Biology, James Cook University, Townsville, Queensland 4811, Australia *Email: d.crossman@auckland.ac.nz ABSTRACT: Nominally herbivorous acanthurids (surgeonfishes) and scarids (parrotfishes) have often been considered a ‘homogeneous’ functional group that consumes and digests algae. Recent work demonstrates that many of these fishes consume detritus. The objective of this study was to investigate the composition of dietary nutrients targeted by these and other fishes in terms of feeding behaviour, diet and short chain fatty acids (SCFA). We undertook a nutritional analysis of a range of species including detritivores, algivores, omnivores and planktivores from north eastern Australia. We calculated assimilation efficiencies for total protein amino acids (TAA), carbohydrate and lipid, and measured TAA in gut fluid along the intestine. Nutrients were assimilated similarly to their dietary proportions, with planktivores assimilating a high proportion of TAA, a moderate proportion of lipid and little carbohydrate. Omnivores assimilated moderate proportions of TAA and carbohydrate, and a low proportion of lipid. Algivores assimilated a low proportion of TAA and lipid, but a high proportion of carbohydrate. Detritivorous scarids and acanthurids differed significantly from algivores, assimilating a high proportion of TAA, a low proportion of carbohydrate and a moderate proportion of lipid. TAA levels in gut fluid of all species were highest in the anterior and lowest in the posterior intestine. Gut segments with highest TAA values were compared between dietary groups and followed a similar trend to TAA assimilation. Planktivores had high concentrations of TAA, while omnivores had intermediate, and algivores the lowest, concentrations. The highest gut fluid TAA concentrations were found in detritivorous scarids and acanthurids, and were significantly higher than in algivores. A significant negative correlation was found between anterior intestinal fluid TAA and posterior intestinal SCFA values. Detritivores had the highest levels of TAA but the lowest levels of SCFA. Planktivorous species had high levels of TAA and low to intermediate levels of SCFA. Omnivores had moderate levels of both TAA and SCFA. Algivores had low levels of TAA but high levels of SCFA. This indicates that there are major differences in the food resources targeted by detritivorous and algivorous fish species on coral reefs. KEY WORDS: Amino acids · Assimilation · Carbohydrate · Coral reefs · Detritus · Herbivorous fishes · Lipid · Trophic strategies Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 296. Online publication date: July 12, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Hull-less Barley Varieties: Storage Proteins and Amino Acid Distribution in Relation to Nutritional Quality

Barley (Hordeum vulgare L.) has had an important impact on human nutrition. Hull-less barley is a genetically improved type that has been widely used in recent years. Six Brazilian hull-less barley varieties (IAC-IBON 214-82; IAC 8612-421; IAC 8501-31; IAC 8501-12; IAPAR 39-ACUMAI; IAC 8501-22) were analyzed for storage protein constituents, amino acid contents, and similarity among the hull-less barley varieties. Albumins, globulins, prolamins I and II, and glutelins were extracted and separated by SDS-PAGE. The total protein amino acid contents of the flour were also determined for each variety by TLC and HPLC. Variations in intensity and appearance and disappearance of protein bands were observed among the varieties suggesting genetic variability. However, the amino acid profile did not indicate any major variations in the amino acid concentrations. The high lysine and threonine total concentrations detected in the seeds of the hull-less barley varieties encouraged an investigation into the regulation of amino acid metabolism and storage protein synthesis.

Hull-less Barley Varieties: Storage Proteins and Amino Acid Distribution in Relation to Nutritional Quality

Abstract Barley (Hordeum vulgare L.) has had an important impact on human nutrition. Hull-less barley is a genetically improved type that has been widely used in recent years. Six Brazilian hull-less barley varieties (IAC-IBON 214-82; IAC 8612-421; IAC 8501-31; IAC 8501-12; IAPAR 39-ACUMAI; IAC 8501-22) were analyzed for storage protein constituents, amino acid contents, and similarity among the hull-less barley varieties. Albumins, globulins, prolamins I and II, and glutelins were extracted and separated by SDS-PAGE. The total protein amino acid contents of the flour were also determined for each variety by TLC and HPLC. Variations in intensity and appearance and disappearance of protein bands were observed among the varieties suggesting genetic variability. However, the amino acid profile did not indicate any major variations in the amino acid concentrations. The high lysine and threonine total concentrations detected in the seeds of the hull-less barley varieties encouraged an investigation into the regulation of amino acid metabolism and storage protein synthesis.

Strategy for analysis of cardiac troponins in biological samples with a combination of affinity chromatography and mass spectrometry.

Cardiac troponins are modified during ischemic injury and are found as a heterogeneous mixture in blood of patients with cardiovascular diseases. We present a strategy to isolate cardiac troponins from human biological material, by use of affinity chromatography, and to provide samples ready for direct analysis by mass spectrometry. Cardiac troponins were isolated from human left ventricular tissue by affinity chromatography. Isolated troponins were either eluted and analyzed by Western blot or enzymatically digested while bound to affinity beads. The resulting peptide mixture was subjected to mass spectrometry for protein identification and characterization. The same method was used to analyze serum from patients with acute myocardial infarction (AMI). Affinity chromatography with antibodies specific for one cardiac troponin subunit facilitated the isolation of the entire cardiac troponin complex from myocardial tissue. The three different proteases used for enzymatic digestion increased the total protein amino acid sequence coverage by mass spectrometry for the three cardiac troponin subunits. Combined amino acid sequence coverage for cardiac troponin I, T, and C (cTnI, cTnT, cTnC) was 54%, 48%, and 40%, respectively. To simulate matrix effects on the affinity chromatography-mass spectrometry approach, we diluted tissue homogenate in cardiac troponin-free serum. Sequence coverage in this case was 44%, 41%, and 19%, respectively. Finally, affinity chromatography-mass spectrometry analysis of AMI serum revealed the presence of cardiac troponins in a wide variety of its free and/or complexed subunits, including the binary cTnI-cTnC and cTnI-cTnC-cTnT complexes. Affinity chromatography-mass spectrometry allows the extraction and analysis of cardiac troponins from biological samples in their natural forms. We were, for the first time, able to directly confirm the presence of cardiac troponin complexes in human serum after AMI. This approach could assist in more personalized risk stratification as well as the search for reference materials for cardiac troponin diagnostics.

Food safety and amino acid balance in processed cassava "Cossettes".

Processed cassava (Manihot esculenta Crantz) roots provide more than 60% of the daily energy intake for the population of the Democratic Republic of Congo. Insufficiently processed cassava roots in a diet deficient in sulfur amino acid have been reported to cause the irreversible paralytic disease konzo, afflicting thousands of women and children in the remote rural areas of Bandundu Province. "Cossettes" (processed cassava roots) purchased in several markets of Kinshasa were analyzed for their content of cyanogens, free amino acids, and total protein amino acids. Residual cyanogen levels were below the safe limit recommended by the codex FAO/WHO for cassava flour (10 mg kg(-1)). The amino acid score was evaluated. Lysine and leucine were the limiting amino acids. Methionine content was very low and contributed about 13% of the total sulfur amino acids. Dietary requirements for sulfur amino acids need to be adjusted for the loss caused by cyanogen detoxification.

Amino acids in seeds and seedlings of the genus Lens

The amino acid content of seeds and 4-day-old seedlings were studied in five species of lentil: Lens culinaris, L. orientalis, L. ervoides, L. nigricans and L. odemensis. Free amino acid and also total protein amino acid content after HCl hydrolysis were determined by HPLC. The nonprotein UV-absorbing amino acids were determined by capillary zone electrophoresis (CZE). The content of free protein amino acids in seeds varied among species and increased dramatically after germination. Asparagine is quantitatively most important in both seed and seedling. The content of free nonprotein amino acids is variable in seeds and seedlings. γ-Hydroxyarginine, γ-hydroxyornithine, α-aminobutyric acid and taurine were found in both seeds and seedlings. Homoarginine was found in four species but not in L. orientalis while γ-aminobutyric acid (GABA), α-aminoadipic acid (α-aaa) and three isoxazolinone derivatives: β-(isoxazolin-5-on-2-yl)-alanine (BIA), γ-glutamyl-BIA (γ-glu-BIA) and 2-carboxymethyl-isoxazolin-5-one (CMI) were found exclusively in the seedlings. CMI was identified for the first time in lentil species. Lathyrine, β-(2-amino-pyrimidine-4-yl)-alanine, which was reported to be in the seeds of some Lathyrus species was confirmed to be present also in the seedling of L. culinaris (trace amount), L. nigricans and L. odemensis. Trigonelline ( N-methyl-nicotinic acid), a plant hormone, is present both in seeds and seedlings in different concentrations except in L. ervoides. The different combination of nonprotein amino acids among the species gives indication of their genetic relationship and might partly explain the varying compatibility for interspecies crossing.

Rotational Echo Double Resonance Detection of Cross-links Formed in Mussel Byssus under High-Flow Stress

13C2H rotational echo double resonance NMR has been used to provide the first evidence for the formation of quinone-derived cross-links in mussel byssal plaques. Labeling of byssus was achieved by allowing mussels to filter feed from seawater containing L-[phenol-4-13C]tyrosine and L-[ring-d4]tyrosine for 2 days. Plaques and threads were harvested from two groups of mussels over a period of 28 days. One group was maintained in stationary water while the other was exposed to turbulent flow at 20 cm/s. The flow-stressed byssal plaques exhibited significantly enhanced levels of 5, 5'-di-dihydroxyphenylalanine cross-links. The average concentration of di-dihydroxyphenylalanine cross-links in byssal plaques is 1 per 1800 total protein amino acid residues.

Cellular immunosuppressive protein in the plasma of parasitized insect larvae.

Evidence that endoparsitoid wasps may suppress the host cellular defense reaction in order to survive within the hemocoel of their host insects was obtained by isolating a cellular immunosuppressive factor from the larval plasma (hemolymph without cells) of the armyworm Pseudaletia separata parasitized with the wasp Cotesia kariyai. The purified proteinaceous factor suppresses hemocyte degranulation and subsequent immune reactions such as nodule formation and encapsulation in the armyworm larvae. The immunosuppressive protein exists not only in the plasma of parasitized larvae but also in the plasma of unparasitized larvae. However, its concentration is much less in unparasitized than in parasitized larvae. Purification procedures involved gel exclusion, ion exchange, and reversed phase high performance liquid chromatography (HPLC). Gel exclusion HPLC and SDS-polyacrylamide gel electrophoresis suggest an approximately 470-kDa hexamer composed of identical subunits of 82 kDa. Aryl amino acids such as tyrosine and phenylalanine comprise about 20% of the total protein amino acid. The sequence of 28 amino acid residues at the amino terminus of the factor was determined to be as follows: Ser-Val-Val-Pro-Thr-Lys-His-Glu-Ile-Lys-Val-Lys-Ala-Val-Glu- Pro-Gln-Tyr-Ile-Xaa-Tyr-Gln-Arg-Lys-Ile-Leu-Ala-Leu-Phe.

Amino acid content in several brain regions of the active and hibernating frog, Rana esculenta

1. 1. Total free amino acid contents in the optic lobe and diencephalon increased significantly during hibernation. 2. 2. Free glutamate + glutamine showed significant increases in the cerebral hemisphere, optic lobe, medulla oblongata and diencephalon. 3. 3. Free aspartate + asparagine showed significant increases in the cerebral hemisphere, optic lobe, diencephalon and olfactory lobe. 4. 4. GABA showed a significant change only in the medulla oblongata. 5. 5. Total protein amino acid level in the cerebellum and olfactory lobe decreased significantly during hibernation and most of the amino acids decreased significantly in these regions. 6. 6. The amino acid metabolism during amphibian hibernation differs from that of the mammal.

Cyclic fluctuations in arylphorin, the principal serum storage protein of Lymantria dispar, indicate multiple roles in development

Arylphorin (Ap) was isolated and partially characterized from larval serum of the gypsy moth, Lymantria dispar (Lepidoptera: Lymantriidae). Non-denaturing and SDS-polyacrylamide gel electrophoresis suggest a 440,000 Da hexamer composed of nonidentical subunits of M r 73,000 and 80,000. Tyrosine and phenylalanine comprise 15.6% of the total protein amino acid. L. dispar Ap is immunologically related to Manduca sexta Ap. Hemolymph Ap concentrations throughout the larval stadia were determined using quantitative immunoelectrophoresis. Cyclic fluctuations in hemolymph concentrations are correlated with each molting cycle. A general increase in Ap concentration during each intermolt is followed by a sharp decline between apolysis and ecdysis. The last days of each instar were found to be the best time to sample protein titer with minimum variance. Hemolymph space, estimated by measuring the dilution of an injected foreign protein, is a constant 28% (v/w) of body weight. Total serum Ap per animal was calculated. A divergent allometric relationship between Ap accumulation and weight gain throughout the larval period results in the ultimate domination of the serum protein profile by Ap in the ultimate larval instar of the female in particular. An additional instar of Ap accumulation in the female gypsy moth is suggested to compensate for the lack of a predominantly female-specific storage protein in this species.

Changes in nitrogen content and amino acid composition of navel oranges during ripening

AbstractNitrogen content and composition of amino acids in juice and rind of navel oranges were studied. The compared varieties were ‘Navelina’ ‘Washington Navel’ and ‘Navelate’, early, mid‐season and late types, respectively. Total N content in juice increased during the season with values from about 60 to near 100 mg 100 ml−1 in Navelina and ‘Washington Navel’ and from 60 to about 80 mg 100 ml−l in ‘Navelate’; amino N increased from 30 to 60 mg 100 ml−lapproximately in the three varieties. The total N content in rind was quite similar in all cases, with values that decreased with time from 1 to around 0·6 g 100 g−l dry weight (DW), 50–60% corresponding to the protein N. The main free amino acids in juice and rind at different maturity stages are tabulated. Proline represents at maturity around 50% of the total free amino acids in rind, with values near to 1·5 mmol 100 ml−l in juice and over 5·0 mmol 100 g−1 DW in rind. Total protein amino acids in rind decreased during maturation, reaching final values of about 20 mmol 100 g−1 DW. Differences in composition among the three studied varieties are discussed.

High-performance liquid chromatography with photochemical fluorimetric detection of tryptophan based on 4-fluoro-7-nitrobenzo-2-oxa- 1,3-diazole : Total protein amino acid analysis

The simultaneous determination of amino acids including trytophan is described. The NBD- F forms a single adduct with tryptophan as with other amino acids, but the adduct lacks intrinsic fluorescence. After ultraviolet irradiation, the adduct fluoresces (pale-green); the fluorescence intensity increases with increasing irradiation time at pH 2-10, Under the same conditions, the other amino acid adducts are slowly decomposed. When the tryptophan adduct, separated on a Nucleosil ODS column (150×4.6 mm, 6 μm), is irradiated in an on-line photochemical reactor (310 nm), its fluorescence peak appears between those of the phenylalanine and lysine adducts. The detection limit for tryptophan by the proposed method is 3 pmol; the limits for other amino acids are 10–100 fmol.

Diel Production and Microheterotrophic Utilization of Dissolved Free Amino Acids in Waters Off Southern California

Diel patterns of dissolved free amino acid (DFAA) concentration and microheterotrophic utilization were examined in the spring and fall of 1981 in euphotic waters from the base of the mixed layer off the southern California coast. The average depths of the isotherms sampled were 19.2 m for spring and 9.0 m for fall. Total DFAA levels were generally higher in the spring than in the fall, 18 to 66 nM and 14 to 20 nM, respectively. Two daily concentration maxima and minima were observed for total DFAAs as well as for most individual DFAAs. Maxima were usually measured in the mid-dark period and in the early afternoon; minima were typically observed in early morning and late afternoon. Bacterial cell numbers reached maximal values near midnight in both seasons. These increases coincided with one of the total DFAA maxima. The second total DFAA maximum occurred in early to midafternoon, during the time of maximum photosynthetic carbon production and rapid dissolved amino acid utilization. Microbial metabolism (incorporation plus respiration) of selected H-amino acids was 2.7 to 4.1 times greater during the daylight hours. DFAA turnover times, based on these metabolic measurements, ranged between 11 and 36 h for the amino acids tested, and rates were 1.7 to 3.7 times faster in the daylight hours than at night. DFAA distributions were related to primary production and chlorophyll a concentrations. Amino acids were estimated to represent 9 to 45% of the total phytoplankton exudate. Microheterotrophic utilization or production of total protein amino acids was estimated as 3.6 mug of C liter day in spring and 1.9 mug of C liter day in the fall. Assimilation efficiency for dissolved amino acids averaged 65% for marine microheterotrophs.

Effect of salting and roasting on the carbohydrates and proteins of Iranian pistachio kernels

SummaryThe free sugars which make up 2.7% of Iranian pistachio cv Badami were identified as fructose, glucose, sucrose, maltose, isomaltose, cellobiose, raffinose and stachyose. Both protein and free amino acids contained the same seventeen amino acids but lacked tryptophan, asparagine and glutamine. After salting and roasting, total available carbohydrates, total starches and dextrins, and total free sugars all decreased compared to controls, as did a number of individual sugars, especially the reducing sugars. While free amino acids had severely decreased, total protein amino acids and individual protein amino acid were not affected at all. The decreases in reducing sugars and in free amino acids may be due in part to their taking part in Maillard reactions.

Purification and properties of manducin, an amino acid storage protein of the haemolymph of larval and pupal Manduca sexta

Manducin, a storage protein, has been isolated from the haemolymph of the tobacco hornworm, Manduca sexta. Cross-linking experiments indicate that the intact protein (mol. wt 540,000) consists of six subunits and has associated with it ca. 2% by weight of lipids. The major lipids are phospholipids, 1, 2-diglycerides and cholesterol. The protein has 3.5% covalently bound sugar, consisting of N-acetylglucosamine and mannose in a molar ratio of two to five. The aromatic amino acids, phenylalanine and tyrosine, make up 20% of the total protein amino acid, while the cysteine content is only 0.4%. SDS polyacrylamide gel electrophoresis shows two closely spaced protein bands of equal intensity with estimated mol. wts corresponding to 87,000 and 92,000. The nature of the differences between these protomers and their distribution in the intact protein is not clear. The occurrence of manducin throughout the life cycle of the animal was followed by quantitative rocket immunoelectrophoresis. The protein is present in early larval instars, but increases dramatically in the last larval instar until it constitutes at least 80% of the total haemolymph proteins. It remains high in the pupa, but decreases to zero during formation of the adult. Thus manducin appears to be a storage form for amino acids sequestered during larval life to be used for construction of the adult animal.

Studies on the constituents of higher fungi of Korea (XX)

To investigate constituents ofStrobilomyces floccopus (Fr.) Karst. andCoprinus comatus (Fr.) S.F. Gray, free and total amino acids of the two mushrooms were quantitatively analyzed by G.L.C. and an amino acid analyzer. Free amino acids were extracted from both mushrooms with ethanol. Fourteen free amino acids were detected from the ethanol extract ofS. floccopus and fifteen free amino acids fromC. comatus by G.L.C. And the dry carphopores of both mushrooms were hydrolyzed with hydrochloric acid and then the total protein amino acids were analyzed by A.A.A. Seventeen total amino acids were detected from each acid-hydrolysate ofS. floccopus andC. comatus. Lipids were extracted from the carpophores ofS. floccopus and saponified with alcoholic potassium hydroxide. The isolated sterols were subjected to G.L.C. and two sterols were detected. The isolated free fatty acids were methylated with diazomethane and subjected to column chromatography and G.L.C. Eleven saturated and nine unsaturated free fatty acids were detected from the carpophores ofS. floccopus. The presence of these nutrient components shows that the two mushrooms can be utilized as edible ones.

Synthesis and Interconversion of Amino Acids in Developing Cotyledons of Pea (Pisum sativum L.)

Freshly isolated cotyledons from 10-day developing pea (Pisum sativum) seeds were fed radiolabeled precursors for 5 hours, and the specific radioactivity of the free and total protein amino acids was determined using a dansylation procedure. When the seven most abundant amino acids in phloem exudate of pea fruits (asparagine, serine, glutamine, homoserine, alanine, aspartate, glycine) were fed singly, their carbon was distributed widely among the aliphatic amino acids, proline and tryptophan; sporadic labeling of tyrosine and histidine also occurred. Feeding of glucose led to relatively greater labeling of aromatic amino acids including phenylalanine. The data support the involvement of known plant pathways in these interconversions. Labeling patterns were consistent with participation of the cyanoalanine pathway in the conversion of serine to homoserine, and with the synthesis of histidine from adenosine. All of the labeled amino acids were incorporated into protein.

The nature of the polypeptide chain termination signal

An experiment was carried out to test whether UAA and UAG are used as termination signals for polypeptide synthesis in Escherichia coli. Amber and ochre mutants which suppress these triplets for premature polypeptide chain termination by inserting tyrosine residues were used. We have detected the misreading of the natural chain termination signals by measuring the amount of extra C-terminal tyrosine inserted by tyrosine-inserting UAA and UAG suppressor strains of E. coli. The experiment was designed to yield a positive result only if there is a termination signal in addition to the UAA or UAG termination triplet. The experiments show that UAG as well as UAA is used as a natural polypeptide chain-termination triplet. Sometimes these triplets are immediately followed by an additional termination signal. It is suggested that polypeptide chain-termination signals are often two nonsense triplets in tandem, as observed in the case of the R17 coat gene by Nichols (1970). In the course of carrying out these experiments, we found that the amino acid distribution at the C-terminus of E. coli proteins seems to be about the same as the natural abundance of the amino acids in total protein. In addition, the proteins of strains containing a nonsense suppressor transfer RNA do not have a measurably larger molecular weight distribution than wild-type E. coli.