The Use of Ascorbate as an Oxidation Inhibitor in Prebiotic Amino Acid Synthesis: A Cautionary Note

It is generally thought that the terrestrial atmosphere at the time of the origin of life was CO₂-rich and that organic compounds such as amino acids would not have been efficiently formed abiotically under such conditions. It has been pointed out, however, that the previously reported low yields of amino acids may have been partially due to oxidation by nitrite/nitrate during acid hydrolysis. Specifically, the yield of amino acids was found to have increased significantly (by a factor of several hundred) after acid hydrolysis with ascorbic acid as an oxidation inhibitor. However, it has not been shown that CO₂ was the carbon source for the formation of the amino acids detected after acid hydrolysis with ascorbic acid. We therefore reinvestigated the prebiotic synthesis of amino acids in a CO₂-rich atmosphere using an isotope labeling experiment. Herein, we report that ascorbic acid does not behave as an appropriate oxidation inhibitor, because it contributes amino acid contaminants as a consequence of its reactions with the nitrogen containing species and formic acid produced during the spark discharge experiment. Thus, amino acids are not efficiently formed from a CO₂-rich atmosphere under the conditions studied.     

The structure of rice storage protein glutelin precursor deduced from cDNA

The complete amino acid sequence of rice storage protein glutelin was determined by the sequencing of the corresponding cDNA. The deduced glutelin precursor has a 37 amino acid signal peptide sequence at the NH₂ terminus, which is followed by a 269 amino acid acidic subunit (M_r = 32 489) and a 193 amino acid basic subunit (M_r = 19 587). The glutelin precursor sequence is homologous to those of pea legumin and soybean glycinin.     

KINETICS OF COMPETITIVE INHIBITION OF NEUTRAL AMINO ACID TRANSPORT ACROSS THE BLOOD-BRAIN BARRIER

The transport of tryptophan across the blood-brain barrier is used as a specific example of a general approach by which rates of amino acid influx into brain may be predicted from existing concentrations of amino acids in plasma. The kinetics of inhibition of [¹⁴C]tryptophan transport by four natural neutral amino acids (phenylalanine, leucine, methionine, and valine) and one synthetic amino acid (α-methyl tyrosine) is studied with a tissue-sampling, single injection technique in the barbiturate-anesthetized rat. The equality of the K₁ (determined from cross-inhibition studies) and the K_m (determined from auto-inhibition data) for neutral amino acid transport indicate that these amino acids compete for a single transport site in accordance with the kinetics of competitive inhibition. Based on equations derived for competitive inhibition, apparent K_m values are computed for the essential neutral amino acids from known data on amino acid transport K_m and plasma concentrations. The apparent K_m values make possible predictions of the in vivo rates of amino acid influx into brain based on given plasma amino acid concentrations. Finally, a method is presented for determining transport constants from saturation data obtained with single injection techniques.     

Spectroscopic characterization of amino acid and amino acid ester-Schiff-base complexes of oxovanadium and their catalysis in sulfide oxidation

α-Amino acid Schiff-base complexes of oxovanadium(IV), whose ligands have amino acid side chains with coordinating functional groups, retained coordination geometries in which the amino acid side chains were probably coordinated in the axial position with a phenolate oxygen, a carboxylate oxygen, an imine nitrogen, and a solvent being bound in the equatorial plane. As for amino acid ester Schiff-base complexes, the amino acid side chains were coordinated in the equatorial plane in the place of the carboxyl group in the case of the amino acid Schiff-base complexes. The amino acid Schiff-base complexes of oxovanadium(V) were present as dimers in dichloromethane. Peroxo complexes prepared from the Schiff-base complexes of oxovanadium(V) converted methyl phenyl sulfide to the corresponding sulfoxide in 80-90% yield in CDCl₃ and in 30-70% yield in CD₃OD in 30 min. They converted the sulfide in a stereoselective manner yielding the sulfoxide in small enantiomeric excess (5-20%).     

The establishment of essential and metabolically derived amino acid profiles in developing chick embryo organs

The accumulation of certain essential and metabolically derived amino acids in the free amino acid pools of three excitable tissues has been studied in the chick embryo. Valine together with leucine are at the onset present in the yolk at higher concentrations than any of the other essential amino acids. By 15 days all the amino acids studied have accumulated in the embryonic pools at a higher rate than valine, although certain amino acids, such as phenylalanine or methionine, always remain at lower relative concentrations than valine. This reflects their low supply in the yolk, rather than a more rapid rate of disappearance (utilization). During early embryogenesis (E₂–E₄), tissues preferentially concentrate glutamic acid, besides taurine and phosphoethanolamine (6). The next distinct stage of development (E₄–E₇) is marked in the brain by a gradual rise in glutamic acid, glutamine and aspartic acid; the same three amino, acids do not demonstrate a further increase in the pool of the heart, while in the whole eye the amino acid profile begins to resemble the blood. Leucine in all three tissues declines rapidly, to reach isoleucine levels by day 7 of development; tyrosine increases slowly in apparent reciprocity to an equally gradual phenylalanine decrease. Into the second week of embryo growth (E₇–E₁₅), GABA appears in the mesencephalon (E₇) and the eye (E₉–E₁₀). In the mesencephalon, the free amino acid pool composition exhibits a rather sudden increase of most metabolically derived amino acids. Glutamic acid and glutamine in the brain increase in parallel; the rate of GABA and aspartic acid accumulation is slower, and for GABA stabilizes on day 14, as does glutamine. In the eye, by day 15, GABA levels are more closely aligned with the aspartic acid content. Finally, throughout embryogenesis serine fluctuations in blood and tissues are in parallel with those of threonine, and different from glycine or alanine which also change in tandem.     

Design and Structure--Activity Relationship of Novel Endothelin Receptor A Tripeptide Antagonists

Summary Novel tripeptides possessing different N-terminal chemical moieties (R) and a series of unnatural amino acids were synthesized as endothelin (ET) receptor antagonists. A number of them showed potent activity in preventing the contraction of rat aortic smooth muscle induced by ET-1. The structure-activity relationships (SAR) of the antagonists were studied in detail and conclusions drawn regarding the optimum design of the pharmacophore. Specifically, the R group has a crucial function in improving peptide selectivity and affinity for the ET receptor. Additionally, the first amino acid AA₁ has a high dependency for a hydrophobic residue, the second amino acid AA₂ can be aromatic hydrophobic amino acid, and the third amino acid AA₃ must be D-isomer.     

Nonprotein amino acid composition of flatpea (Lathyrus sylvestris L.) as affected by ethephon seed treatments and seedling fertilization

Use of flatpea (Lathyrus sylvestris L.) as a forage is limited because of nonuniform seed germination and the potentially toxic effects of 2,4-diaminobutyric acid (A₂bu), a nonprotein amino acid found in seeds and vegetative tissues. The effects of ethephon (2-chloroethyl phosphonic acid) on seed germination, amino acid leachates of seeds, and amino acid composition (particularly A₂bu) of seedlings were investigated. Germination of flatpea seeds, imbibed for 16 h in 0, 100, 200, 400, 800, and 1600 mg/L ethephon, did not differ, but amino acid leachates tended to increase up to 200 mg/L ethephon and then decline at higher concentrations. The major amino acid constituents in leachates were A₂bu, 4-aminobutyric acid (Abu), and homoserine (Hse). Dry matter accumulation of seedlings grown from ethephon-treated seeds was reduced for second cuttings grown from ethephon-treated seeds and high nitrogen grown plants. During regrowth, free amino acid accumulation was most pronounced in leaves of plants supplied with high nitrogen. The most abundant free amino acids in flatpea tissues were the same as those in seed leachates, but concentration and relative abundance varied with nitrogen level, plant part, and ethephon treatment. Results suggest that ethephon seed treatments can have persistent effects on the growth and amino acid composition of flatpea seedlings grown under different nitrogen regimes.     

Nonprotein amino acid composition of flatpea (Lathyrus sylvestris L.) as affected by ethephon seed treatments and seedling fertilization

Use of flatpea (Lathyrus sylvestris L.) as a forage is limited because of nonuniform seed germination and the potentially toxic effects of 2,4-diaminobutyric acid (A₂bu), a nonprotein amino acid found in seeds and vegetative tissues. The effects of ethephon (2-chloroethyl phosphonic acid) on seed germination, amino acid leachates of seeds, and amino acid composition (particularly A₂bu) of seedlings were investigated. Germination of flatpea seeds, imbibed for 16 h in 0, 100, 200, 400, 800, and 1600 mg/L ethephon, did not differ, but amino acid leachates tended to increase up to 200 mg/L ethephon and then decline at higher concentrations. The major amino acid constituents in leachates were A₂bu, 4-aminobutyric acid (Abu), and homoserine (Hse). Dry matter accumulation of seedlings grown from ethephon-treated seeds was reduced for second cuttings grown from ethephon-treated seeds and high nitrogen grown plants. During regrowth, free amino acid accumulation was most pronounced in leaves of plants supplied with high nitrogen. The most abundant free amino acids in flatpea tissues were the same as those in seed leachates, but concentration and relative abundance varied with nitrogen level, plant part, and ethephon treatment. Results suggest that ethephon seed treatments can have persistent effects on the growth and amino acid composition of flatpea seedlings grown under different nitrogen regimes.     

Neutral amino acid transport by marine fish intestine: role of the side chain

This work was devoted to the study of the structure-affinity relationships in neutral amino acid transport by intestinal brush border of marine fish (Dicentrarchus labrax). The effects of the length of the side chain on kinetics of glycine, alanine, methionine and amino isobutyric acid were investigated. In the presence of K⁺ two components were characterized: one is saturable by increased substrate concentrations, whereas the other can be described by simple diffusion mechanism. Simple diffusion, a passive, non-saturable, Na⁺-independent route, contributes largely to the transport of methionine and to a much lesser extend to alanine, glycine or alphaaminoisobutyric acid uptakes. If a branched chain is present, as in the case of amino isobutyric acid, diffusion is low. A Na⁺-independent, saturable system has been fully characterized for methionine, but not for branched amino acids such as amino isobutyric acid. In the presence of Na⁺ saturable components were shown. Two distinct Na⁺-dependent pathways have been characterized for glycine uptake, with low and high affinities. For alanine and methionine only one Na⁺-dependent high affinity system exists with the same half-saturation concentration and the same maximum uptake at saturable concentrations. Glycine high affinity system has the same half-saturation concentration as methionine or alanine uptake, whereas maximum uptake is lower. The substitution of the hydrogen by a methyl group results in a severe decrease of uptake (aminoisobutyric acid). Mutual inhibition experiments indicate that the same carriers could be responsible for methionine and alanine uptakes and probably glycine Na⁺-dependent uptake. The influence of Na⁺ concentrations (100^-1 mol·l^-1) on amino acid uptake was examined. Glycine, alanine, methionine and amino isobutyric acid transport can be described by a hyperbolic function, with a saturation uptake which is highly increased for methionine. However, the half-saturation concentration does not seem to be strongly affected by the amino acid structure. The effect of Na⁺ concentration (25 and 100 mmol·l^-1) on the kinetics of methionine uptake have been also examined. The maximum uptake of the saturable system clearly shows a typical relationship with concentration.Abbreviations [AA] amino acid concentration - AIB aminoisobutyric acid - [I] Inhibitor amino acid concentration - J _i uptake in the presence of inhibitor - J _o uptake without inhibitor - K _d passive diffusion constant - K _i inhibitor constant - K _t concentration of test amino acid for half-maximal flux - MES 2[N-morpholino]ethanesulphonic acid - V _max maximum uptake at saturable amino acid concentrations - V _tot total amino acid uptake     

Role of 1α,25(OH)2 vitamin D3 on α-[1-C]MeAIB accumulation in immature rat testis

1,25D₃ is critical for the maintenance of normal reproduction since reduced fertility is observed in male rats on a vitamin D-deficient diet. Vitamin D-deficient male rats have incomplete spermatogenesis and degenerative testicular changes. In the present study we have examined the ionic involvement and intracellular messengers of the stimulatory effect of 1,25D₃ on amino acid accumulation in immature rat testis. 1,25D₃ stimulates amino acid accumulation from 10⁻¹² to 10⁻⁶ M by increasing the slope to reach a maximum value at 10⁻¹⁰ M, as compared to the control group. No effect was observed at a lower dose (10⁻¹³ M). Time-course showed an increase on amino acid accumulation after 15, 30, and 60 min of incubation with 1,25D₃ (10⁻¹⁰ M). 1,25D₃ stimulated amino acid accumulation in 11-day-old rat testis but not in testis that were 20 days old. Cycloheximide totally blocked the 1,25D₃ action on amino acid accumulation. Furthermore, a localized elevation of cAMP increased the stimulatory effect of 1,25D₃ and the blockage of PKA nullified the action of the hormone. In addition, 1,25D₃ action on amino acid accumulation was also mediated by ionic pathways, since verapamil and apamine diminished the hormone effect. The stimulatory effect of 1,25D₃ on amino acid accumulation is age-dependent and specific to this steroidal hormone since testosterone was not able to change amino acid accumulation in both ages studied. This study provides evidence for a dual effect for 1,25D₃, pointing to a genomic effect that can be triggered by PKA, as well as to a rapid response involving Ca²⁺/K⁺ channels on the plasma membrane.     

Physiological studies on Phymatotrichum omnivorum X. Influence of nitrogen sources on free and bound amino acid pools

The effect of nitrogen source on the free and bound amino acids of mycelium of Phymatotrichum omnivorum (Shear) Dugg was investigated. The largest free amino acid pool was present in the natural medium and the smallest in the synthetic medium. Phymatotrichum omnivorum was able to utilize different nitrogen sources with the best growth occurring with NH₄NO₃. The ratio of glycine to alanine and aspartic to glutamic was around 0.25 in the free amino acid pool and around 1 in the bound amino acid pool. The free pool of glutamic acid ranged from 5.6 % to 27.2 % depending upon the nitrogen source in the media. The free pool of alanine ranged from 35.7 % to 17.2 % in relation to the nitrogen source. Most other amino acid ratios did not vary significantly between the free amino acids and the bound amino acids.     

Submerged culture conidial germination and conidiation of the bioherbicideColletotrichum truncatum are influenced by the amino acid composition of the medium

Summary Submerged culture experiments were conducted to determine the optimal nitrogen source for rapidly producing conidia of the bioherbicide,Colletotrichum truncatum. Germination ofC. truncatum conidial inocula in submerged culture occurred most rapidly (>95% in 6 h) in media provided with a complete complement of amino acids. When (NH₄)₂SO₄, urea, or individual amino acids were provided as the sole nitrogen source, conidial germination was less than 20% after 6 h incubation. Conidia production was delayed inC. truncatum cultures grown in media with urea or individual amino acids as nitrogen sources compared to cultures supplied with Casamino acids or complete synthetic amino acid nitrogen sources. The use of methionine, lysine, tryptophan, isoleucine, leucine or cysteine as a sole nitrogen source severely inhibitedC. truncatum conidia production. Media with synthetic amino acid mixtures less these inhibitory amino acids produced significantly higher conidia yields compared to media with amino acid mixtures containing these amino acids. When various amounts of each individual inhibitory amino acid were added to media which contained amino acid mixtures, cysteine and methionine were shown to be most effective in reducing conidiation. An optimal nitrogen source forC. truncatum conidiation in submerged culture should contain a complete mixture of amino acids with low levels of cysteine, methionine, leucine, isoleucine, lysine and tryptophan for rapid conidiation and optimal conidia yield.The mention of firm names or trade products does not imply that they are endorsed or recommended by the US Department of Agriculture over other firms or similar products not mentioned.     

Preliminary Genetic Studies of the Phenotype of Betaine Deficiency in Zea mays L

Glycinebetaine-deficient inbreds of Zea mays do not exhibit a general deficiency of nitrogenous solutes; the total free amino acid levels of betaine-deficient lines are not significantly less than those of inbreds which exhibit >100-fold higher betaine levels. Betaine-deficient inbreds are characterized by extremely low betaine: total free amino acid ratios (<0.0015). Highly significant correlations are demonstrated between the expected mid-parent and observed betaine:amino acid ratios of 30 hybrids of known pedigree. In 12 hybrids constructed from a betaine-deficient male parent (inbred 1506), the observed betaine:amino acid ratios of the hybrids are proportional to the betaine:amino acid ratios of the female parents (r = 0.83). Two hybrids, 1146 × 1074 and 1146 × 1506, were chosen for further genetic analysis. The common female parent (1146) and inbred 1074 both exhibit betaine:amino acid ratios of 0.090, a value which is approximately 90-fold greater than the betaine:amino acid ratio of inbred 1506. Hybrid 1146 × 1074 exhibits almost exactly twice the betaine:amino acid ratio of hybrid 1146 × 1506. If inbred 1506 is homozygous recessive for a single nuclear gene responsible for the phenotype of betaine deficiency, and if inbreds 1146 and 1074 are homozygous dominant for this allele, then this twofold difference in betaine:amino acid ratio must be associated with the homozygous dominant and heterozygous conditions, respectively, for 1146 × 1074 and 1146 × 1506. Evidence is presented from both greenhouse and field evaluations of F₂ populations of these hybrids that a single nuclear recessive gene is most likely responsible for the phenotype of betaine-deficiency in inbred 1506. Approximately 25% of the F₂ segregants from 1146 × 1506 exhibited extremely low betaine:amino acid ratios (<0.0015), whereas 0% of the F₂ segregants from 1146 × 1074 exhibited this phenotype. The segregation patterns with respect to betaine:amino acid ratio suggest a 1:2:1 segregation ratio for homozygous recessive:heterozygous:homozygous dominant individuals within the 1146 × 1506-F₂ population.     

Renal handling of amino acids in 5/6-nephrectomized rats: Stimulation of renal amino acid reabsorption after treatment with triiodothyronine or dexamethasone under amino acid load

Summary In anaesthetized adult female rats, the renal amino acid handling was measured six days after 5/6 nephrectomy (5/6NX). The distinct rise in blood urea nitrogen as well as the significant reduction in urine flow and GFR indicate an impairment of kidney function. In principle, in 5/6NX rats amino acid plasma concentrations were comparable to those of control animals with two intact kidneys, whereas the fractional excretions (FE_AA) of most endogenous amino acids measured were significantly enhanced. After bolus injection of leucine or taurine (each 20 mg/100 g b.wt.) or glutamine (90 mg/ 100 g b.wt.), dissolved in 2m1 normal saline per 100 g b.wt., the FE_AA of both the amino acids administered and the endogenous amino acids increased as a sign of overloaded amino acid reabsorption capacity. This effect was more pronounced in 5/6NX rats than in controls. As early as one hour after amino acid load, plasma concentrations and FE_AA returned to baseline values of 5/6NX rats. A pretreatment with triiodothyronine (20,µg/100 g b.wt.) or dexamethasone (60 µg/100 g b.wt.), both given intraperitoneally once daily for 3 days, stimulated the renal amino acid transport capacity in 5/6NX rats: the increase in FE_AA after amino acid load was significantly lower compared to non-pretreatred animals. This stimulation could be shown for the bolus amino acids and the endogenous amino acids and was more distinct in 5/6NX rats than in controls with two intact kidneys.     

Enzymatic peptide synthesis by the recombinant proline-specific endopeptidase from Flavobacterium meningosepticum and its mutationally altered Cys-556 variant

Proline-specific endopeptidase (PSE) (EC 3.4.21.26) was investigated for its potential as a catalyst in peptide synthesis. Using an activated peptide ester or a peptide amide as the acyl component, the enzyme catalyzed kinetically controlled aminolysis and transpeptidation respectively, with various amino acid amides as acyl acceptors. To a certain extent the nucleophile preference reflected the amino acid preference in the S₁-position of the enzyme in peptide hydrolysis: the highest fractions of aminolysis were obtained using amino acid amides with hydrophobic side-chains (e.g. Leu-NH₂, Phe-NH₂). PSE also catalyzed the thermodynamically controlled condensation of short peptides with a free carboxyterminus and various amino acid amides. This enabled us to examine the acceptance of different acyl components in the substrate-binding site of the enzyme with regard to their amino acid composition: In the S₁ position proline was clearly favored, but alanine was also accepted, whereas the S₂ subsite accepted various amino acids rather unspecifically. Since PSE was shown to be extremely sensitive against water-miscible organic solvents, an alternative approach was used to increase yields in enzymatic peptide synthesis: a derivative of PSE in which the catalytic Ser-556 is converted to a Cys was constructed by protein engineering. This mutant (PSE_cys) exhibited a dramatically increased peptide ligase activity in aqueous solution.     

Urethane protected amino acid N-carboxyanhydrides and fluorides (U-NCAs and U2AAFs)

Summary In order to obtain peptide analogues containing a central pyrrolide bond, as potential mechanism-based inhibitors of the HIV-1 proteinase, activated derivatives of amino acids were required. Treatment of a N,N-bis(Boc) amino acid pyridinium salt with cyanuric fluoride in dichloromethane furnished the correspondingbis(Boc) amino acid fluoride (Boc₂AAF). Use of the Vilsmeier reagent in acetonitrile, instead of the cyanuric fluoride, led to a N-Boc amino acid N-carboxyanhydride (Boc-NCA). From a mixed N-Z,N-Boc amino acid salt a N-Z,N-Boc amino acid fluoride and a Z-NCA were respectively obtained. The very sensitive Young test showed that during the coupling of the N-benzoyl-L-Leucine N-carboxyanhydride or the N-benzoyl N-Boc-L-leucyl fluoride with ethyl glycinate the degrees of racemization were weak. Owing to the electronegativity and the small size of the fluorine atom, thebis(urethane) amino acid fluorides are efficient acylating agents for amines and pyrrole anions.     

Solid phase and solution synthesis of NvocLys(CO(CH<Subscript>2</Subscript>)<Subscript>5</Subscript>NH–NBD)OCH<Subscript>2</Subscript>CN,a trifunctional fluorescent lysine derivative

Herein, we describe a general strategy for the facile synthesis of a multifunctional amino acid derivative bearing both fluorescent and photolabile groups such as the lysine derivative NvocLys(CO(CH₂)₅NH–NBD)OCH₂CN (1) that can be used as a biophysical tool for studying protein structure. The synthetic strategy involves functionalization of the amine groups while the amino acid is attached to a solid support, followed by esterification of the carboxylic acid in solution. The solid support protects the caboxylic acid, preventing a side reaction associated with the synthesis in solution and obviating the need for chromatographic purification of several intermediates. This synthetic strategy can be used for the preparation of a variety of amino acid derivatives with unusual α-amine and side chain functionalities.     

AMINO ACID TRANSPORT IN NITZSCHIA OVALIS ARNOTT1,2

The marine diatom Nitzschia ovalis possesses at, least 3 amino acid uptake systems, specific for transport of acidic, polybasic, and, neutral amino acids. Maximum uptake velocity (V_max) for each, site is inversely related to the nitrogen content of the cell, and to the nitrogen available in the culture medium. Transport, of polybasic amino acids occurs throughout the course of growth in batch, culture, but the V_max increases dramatically as the culture ages and nitrogen/cell reaches a low value. K_s does not, change significantly. Acidic and neutral amino acids are taken up only by cells harvested from nitrogen-poor culture. It appears that amino acid transport is repressed by high concentrations of nitrogen in the medium. Under natural conditions, where nitrogen concentrations are low, the contribution of amino acid uptake to the nitrogen economy of Nitzschia populations may be significant.     

Patterns of short-term amino acid accumulation and loss in the root-zone of liquid-cultured forage rape (Brassica napus L.)

Amino acid release from roots of sterile and non-sterile, solution-grown, 7-, 21- and 60-days-old forage rape plants (Brassica napus L.), was measured over periods of up to 6 hours. With sterile plants, release of amino acids into a fixed volume of collection medium (6, 12, 70 mL) was concentration-limited, giving rise to similar convex accumulation profiles for individual acids. In contrast, amino acid accumulation in continuously circulating collection medium was not concentration limited, giving a linear accumulation pattern. The compositions of accumulating amino acids, which were similar to those measured in root extracts, did not change significantly. However, the proportions of ALA, GABA, GLU and ILE in both root extracts and root-derived amino acids increased as plants aged. Older plants released more amino acids per plant, while younger plants released more amino acids g^-1 root DW. Using non-sterile plants, the patterns of change in amino acid concentration and composition in the collection medium were completely different from those determined with sterile plants. In general, with 7-days-old plants, and 60-days-old plants that had recently become non-sterile, an initial rise in the concentration of all acids was followed by a fall to low levels. The loss of amino acids was apparently due to microbial consumption. Individual amino acids attained maximum concentration at different times during the collection process. This is attributed mainly to concentration-dependent differential assimilation of amino acids, since those with the highest initial concentrations, the major components of the mixtures released from roots, declined the earliest. When calculated rates of amino acid release from roots (R_r) and microbial consumption of amino acids (R_c) were compared (for 7-days-old plants), the highest ratios of R_c/R_r were found for ASN, ARG, GLU, GLN, and LYS. This suggests a degree of selectivity for glutamate and nitrogen-rich acids on the part of the consuming micro-organisms. With 21-days old plants and 60-days old plants grown entirely under non-sterile conditions, fluctuations in amino acid concentration were similar for all acids.     

Changes in the radioresistance of bacteria after the inhibition of proteosynthesis in the preirradiation phase

The strain ofEscherichia coli WP₂ (try_v) was irradiated with UV light, at a dosage of 240 erg/mm. Proteosynthesis was inhibited by the elimination of the essential amino acid from the cultivation medium. Changes in radioresistance were followed during 45 minutes of starvation and during the subsequent 45 minutes of restitution after the addition of the essential amino acid. The radioresistance of the cells showed a linear increase immediately after the removal of the essential amino acids, proportional to the duration of the inhibition of proteosynthesis. The increase in radioresistance was shown to be reversible. After the addition of the essential amino acid there was an immediate decrease in radioresistance which was most marked in the first 15 minutes.