Sugar and amino acid composition of ant‐attended nectar and honeydew sources from an Australian rainforest

Abstract Ants (Hymenoptera: Formicidae) consume a broad spectrum of liquid food sources including nectar and honeydew, which play a key role in their diet especially in tropical forests. This study compares carbohydrates and amino acids from a representative spectrum of liquid sources used by ants in the canopy and understorey of a tropical rainforest in northern Queensland, Australia. Eighteen floral nectars, 16 extrafloral nectars, two wound sap and four homopteran honeydew sources were analysed using high performance liquid chromatography. Wounds comprised flower abscission scars on Normanbya normanbyi L. H. Bailey and bitemarks on Cardwellia sublimis F. Muell. where ants were actively involved in wounding. Discriminant analysis was performed to model differences between food sources in sugar and amino acid concentration and composition. All characteristics varied significantly among plant species. Honeydew contained a broader spectrum of sugars (including melezitose, raffinose, melibiose, lactose and maltose) than nectar (sucrose, glucose, fructose), but certain extrafloral nectars had similar amino acid profiles and, like honeydew sources, were often monopolized by ants. Most common amino acids across the sources were proline, alanine and threonine among 17 α‐amino acids identified. Interspecific variability concealed characteristic differences in sugar and amino acid parameters between nectar, honeydew and wound sap across all plants, but these types differed significantly when found on the same plant. Among all sources studied, only a few flower nectars were naturally not consumed by ants and they were significantly less attended than sugar controls in feeding trials. These nectars did not differ in sugars and amino acids from ant‐attended flower nectars, suggesting the activity of repellents. Apart from these exceptions, variability in amino acids and carbohydrates is proposed to play a key role in ant preferences and nutrition.     

When good bugs go bad: intraguild predation by Jalysus wickhami on the parasitoid, Cotesia congregata

We report a case of direct intraguild predation involving an insect predator and parasitoid in an agricultural system. The spined stilt bug, Jalysus wickhami Van Duzee, feeds on eggs of the tobacco hornworm, Manduca sexta L., and also on prepupal and pupal stages of the gregarious hornworm parasitoid, Cotesia congregata (Say). In two separate trials, mean mortality of attached parasitoids was significantly lower (66%, 73%) than that of their detached siblings (97%, 96%) after a 3 day exposure to stilt bugs, demonstrating that attachment to the host offered some protection against predation. In no-choice experiments, prepupal parasitoids suffered greater mortality (0 day-old=61%, 1 day-old=65%) than pupal parasitoids (2 day-old=50%, 3 day-old=14%). When offered in combination with 0 or 2 day-old hornworm eggs, respective mortality of 0, 1, 2 and 3-day-old pupal parasitoids showed a similar pattern (67%, 63%, 33% and 23%). In another experiment, mortality of 0-day-old pupal parasitoids (64%) was greater than that of 3 day-old pupal parasitoids (38%). Mortality of pupal parasitoids was not affected by the availability of hornworm eggs, a highly acceptable food. Younger pupal parasitoids (=prepupae) probably suffered greater mortality because they were more easily fed on by stily bugs than older (pupated) ones. Because C. congregata overwinters in the prepupal stage, it may be particularly vulnerable to attack late in the season when stilt bug populations are large and hornworm eggs are relatively uncommon.     

Carbon-nitrogen requirements for the expression of nitrogenase activity in cultured Parasponia-Rhizobium strain ANU 289

Nutritional factors controlling derepression of nitrogenase activity in Parasponia-Rhizobium strain ANU 289 were studied in stationary and agitated liquid cultures. Altering type and/or concentrations of the constituents of the derepression medium in respect of carbon and nitrogen sources influenced both derepression kinetics as well as the maximal level of activity. Hexose sugars and disaccharides stimulated nitrogenase activity three to six-fold compared to pentose sugars. Activity was also modulated by combining sugars with some organic acids such as succinate, fumarate and pyruvate but not with others (e.g. -ketoglutarate, malate, malonate). Of the range of nitrogen sources tested, either casamino acids (at 0.05%, but not at 0.1%), glutamate, proline or to a lesser extent histidine (each at 5 mM N) supported significant derepression of nitrogenase activity. Notably glutamine, urea, alanine, ammonium sulfate, nitrate, nitrite (each at 5 mM N) and yeast extract (0.05%) failed to derepress or support nitrogenase activity. Ammonium (5 mM) abolished established nitrogenase activity of rapidly agitated cultures within 15 h after addition. This inhibitory effect was alleviated by the addition of methionine sulfoximime (10 mM). Thus, in view of strong glutamine effects, ammonium repression appears to be mediated by glutamine and not by ammonium itself.Abbreviations HEPES [4-(2-hydroxyethyl)-1-piperazine-ethane; sulfonic acid] - MOPS [3-(N-morpholino) propane sulphonic acid] - MSX Methionine sulfoximine     

Regulation of branched-chain amino acid biosynthesis in Streptomyces fradiae,a producer of tylosin

Synthesis of threonine dehydratase in Streptomyces fradiae was positively influenced by valine and negatively by isoleucine. However, these two amino acids had no effect on the activity of this enzyme. Synthesis of threonine dehydratase in -aminobutyrate resistant mutants of S. fradiae was pronouncedly less sensitive to the positive effect of valine and this change in regulation led to valine overproduction. Synthesis of acetohydroxy acid synthase is regulated in a similar manner to that of threonine dehydratase, however a lower level of expression was detected in -aminobutyrate resistant mutants. And again, no effect of branched-chain amino acids on acetohydroxy acid synthase activity was observed. It follows that in S. fradiae synthesis of threonine dehydratase is the main regulatory mechanism governing production and the mutual ratio of synthesized valine and isoleucine.Abbreviations -AB -aminobutyrate - AHAS acetohydroxy acid synthase - -KB -ketobutyrate - MNNG N-methyl-N-nitro-N-nitrosoguanidine - TD threonine dehydratase - Trans. B. transaminase of branched-chain amino acids - VDH valine dehydrogenase     

Effect of sugars,amino acids,and culture technique on maturation of somatic embryos of Pinus strobus on medium with two gellan gum concentrations

Maturation of five embryogenic lines of Pinus strobus L. was tested on media with various sugars and sources of organic nitrogen, and solidified with two gellan gum concentrations (0.6 and 1.0%). Mature somatic embryo production was more abundant at 1.0% gellan gum than at 0.6%. Complex combinations of amino acids had little effect on mature embryo production of most tested embryogenic lines. Increasing glutamine concentration of the maturation medium from 1.7 to 7.3 g l⁻¹ was beneficial to one embryogenic line. Increasing sucrose concentration or substituting part of the sucrose with mannitol or sorbitol had variable effects on somatic embryo maturation depending on the embryogenic line. A medium with 88 mM sucrose plus 175 mM sorbitol solidified with 1.0% gellan gum produced high numbers of somatic embryos in four out of five embryogenic lines tested. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of Dietary Components on Larval Life History Characteristics in the Medfly (Ceratitis capitata: Diptera,Tephritidae)

Background

The ability to respond to heterogenous nutritional resources is an important factor in the adaptive radiation of insects such as the highly polyphagous Medfly. Here we examined the breadth of the Medfly’s capacity to respond to different developmental conditions, by experimentally altering diet components as a proxy for host quality and novelty.

Methodology/Principal Findings

We tested responses of larval life history to diets containing protein and carbohydrate components found in and outside the natural host range of this species. A 40% reduction in the quantity of protein caused a significant increase in egg to adult mortality by 26.5%±6% in comparison to the standard baseline diet. Proteins and carbohydrates had differential effects on larval versus pupal development and survival. Addition of a novel protein source, casein (i.e. milk protein), to the diet increased larval mortality by 19.4%±3% and also lengthened the duration of larval development by 1.93±0.5 days in comparison to the standard diet. Alteration of dietary carbohydrate, by replacing the baseline starch with simple sugars, increased mortality specifically within the pupal stage (by 28.2%±8% and 26.2%±9% for glucose and maltose diets, respectively). Development in the presence of the novel carbohydrate lactose (milk sugar) was successful, though on this diet there was a decrease of 29.8±1.6 µg in mean pupal weight in comparison to pupae reared on the baseline diet.

Conclusions

The results confirm that laboratory reared Medfly retain the ability to survive development through a wide range of fluctuations in the nutritional environment. We highlight new facets of the responses of different stages of holometabolous life histories to key dietary components. The results are relevant to colonisation scenarios and key to the biology of this highly invasive species.     

Studies on the biochemistry and fine structure of silica-shell formation in diatoms

Summary The distribution of radioactivity in ethanol-water-soluble compounds after short periods of photosynthetic incorporation of ¹⁴CO₂ is consistent with the operation of the photosynthetic carbon reduction (PCR) cycle in the fresh water diatom Navicula pelliculosa. Incorporation of ¹⁴CO₂ for extended time periods established the presence of the intermediates of the PCR and tricarboxylic acid (TCA) cycles, amino acids, and organic acids; free sugars were not observed. The main labelled soluble carbohydrate was a glucan. Hydrolysis of the radioactive insoluble material indicated the presence of carbohydrates containing several distinct sugars, and proteins with the usual amino-acid composition. During silicon starvation of exponentially growing cultures, rates of incorporation of both ³²P _i and ¹⁴CO₂ decreased. Incorporation into the lipid increased, with a corresponding decrease into protein and carbohydrate. Reintroduction of Si to staryed cells led to an increased rate of incorporation of both isotopes, and transient changes in the radioactivity in most metabolic intermediates investigated. After 30 min the radioactivity in all PCR cycle intermediates, except phosphoglyceric acid, had increased by about 300%. The radioactivity of citrate and -keto-glutarate increased, whereas that of other TCA-cycle intermediates decreased. An initial decrease in the levels of glutamate, aspartate and glutamine was apparently reversed by cleavage of glutamate-aspartate peptides, as radioactivity of other amino acids increased. Incorporation into the soluble glucan and into protein increased markedly although the rate of incorporation into insoluble carbohydrates remained constant.     

Effects of amino acids on methionine-sulfoximine-induced heterocyst formation in Anabaena

Heterocyst development in ammonia-grown cultures of Anabaena variabilis and Anabaena 7120 was fully induced by the amino-acid analog methionine sulfoximine (MSO) at concentrations of 0.5–1.0 M. Glutamine, glutamate, aspartate, and alanine at 0.5 mM blocked the induction of heterocysts by MSO in A. variabilis. With Anabaena 7120, glutamine and glutamate were fully effective and alanine partially effective in preventing MSO-induced heterocyst formation. In MSO-treated algae, glutamine synthetase activity was reduced to less than 15% of control values within 4–6 h. Inactivation of the enzyme was prevented by all four amino acids tested.     

Studies on the putative role ofγ-glutamyl transpeptidase in intestinal transport of amino acids in Atlantic salmon

Summary The -glutamyl cycle is considered to function in the membrane transport of amino acids, particularly glutamine and cysteine. When groups of Atlantic salmon were fed either a control diet containing 45% crude protein or an amino acid diet (of similar overall amino acid composition but containing elevated levels of glutamine and cysteine) for 16 weeks, weight gains were significantly greater in the former group than in those given the amino acid diet. There were no significant differences between treatments in -glutamyl transpeptidase (GT) activity in the proximal intestine; in distal intestine there was significantly more activity in control fish. Mean levels of GSH were higher in tissues (pyloric caeca, distal intestine and kidney) of amino acid diet fish than in those of control fish. Glutamine was less effective as a -glutamyl acceptor than several other amino acids when tested with salmon caecal GT. There were no morphological adaptations to the two feeds. Nutrient uptake studies showed an increased uptake of glutamine, but decreased uptakes of proline and methionine in proximal intestine of salmon fed amino acid diet. Much the greater part of the glutamine uptake, even at high concentrations was shown to be by Na⁺ dependent processes. There is no evidence that GT itself is Na⁺ dependent. The results do not support the view that the -glutamyl cycle and GT in particular are involved in the transport of amino acids in the intestine and are discussed in this context.Abbreviations GT -glutamayl transpeptidase - GSH reduced glutathione     

Synthesis ofO-glycopyranosyl-N-hydroxysuccinimides of glucose and lactose and their opening by nucleophiles into prespacer glycosides

O-Glycopyranosyl-N-hydroxysuccinimides of glucose and lactose have been synthesized. Peracetylated sugars, acetobromo sugars and benzoylated thioethyl glycosides have been used as precursors. With boron trifluoride etherate in dichloromethane, peracetylated sugars gave predominantly the anomer. Trimethylsilyl trifluoromethanesulfonate in nitromethane, however, gave predominantly the anomer. Treatment of the acetylatedO-glucopyranosyl-N-hydroxysuccinimide with various nucleophiles (methoxide, hydroxide and pentylamine) gave the corresponding deacetylatedN-(succinyl)glucopyranosylhydroxylamines in almost quantitative yield. These derivatives are suitable for the formation of glycoconjugates or attachment of carbohydrates to solid phases using the opened succinimide as linking arm.     

Effects of ammonia on carbon metabolism in photosynthesizing isolated mesophyll cells from Papaver somniferum L.

Addition of ammonia to a suspension of photosynthesizing isolated mesophyll cells from P. somniferum quantitatively alters the pattern of carbon metabolism by increasing rates of certain key ratelimiting steps leading to amino-acid synthesis and by decreasing rates of rate-limiting steps in alternative biosynthetic pathways. Of particular importance is the stimulation of reactions mediated by pyruvate kinase and phosphoenolpyruvate carboxylase. The increased rates of these two reactions, which result in an increased flow of carbon into the tricarboxylic-acid cycle, correlate with a rapid rise in glutamine (via glutamine synthetase) which draws carbon off the tricarboxylic-acid cycle as -ketoglutarate. Increased flux of carbon in this direction appears to come mainly at the expense of sucrose synthesis. The net effect of addition of ammonia to mesophyll cells is thus a redistribution of newly fixed carbon away from carbohydrates and into amino acids.     

Carbohydrates,invertase activity,growth and dimorphism inSporisorium reilianum

Sporisorium reilianum, the fungus that causes sorghum head smut, was grown with sucrose, lactose, trehalose or raffinose in liquid suspension or on a solid medium. Liquid culture media were analyzed for hydrolysis products of these carbohydrates to determine extracellular enzyme activity of the fungus. Increased amounts of glucose and fructose in the culture medium ofS. reilianum grown with sucrose or raffinose indicated that invertase (-fructofuranosidase, 3.2.1.26) activity was present. No evidence of extracellular galactosidase or trehalase activity was found. Enhanced sporidial colony formation on carbohydrates that can be hydrolyzed to hexoses, and specific forms of mycelial growth on lactose, trehalose or on a carbohydrate-deficient medium might suggest that mycelial growth is a way of foraging for food sources. However, the rapid and profuse mycelial growth on the host cell wall glycoprotein appears to be in response to abundant food supply (probably of a different type). Therefore availability of different kinds of carbon sources in the environment of the growing fungus might determine dimorphism and associated pathogenesis byS. reilianum.Technical Article No: 30699 from the Texas Agricultural Experiment Station.     

A comparison between the amino acid composition of an egg parasitoid wasp and some of its hosts

Amino acid compositions of the eggs of five lepidopteran hosts for Trichogramma minutum were compared with each other and with a non-host species, Rhodnius prolixus, in which T. minutum oviposits but does not develop. Host eggs are quite homogeneous, particularly when compared according to groupings of potentially interconvertible amino acids. Combined mole percent values for glycine, serine and alanine were higher in hosts (27.5–29.2 mole%) than in R. prolixus eggs (21.5 mole%), in bovine serum albumin (14.9%), which has been used as a protein source in artificial diets for T. minutum, or in many of the mixtures used in published diets for this species. Since these three amino acids make up 26.3 mole% of the adult amino acid content of T. minutum, their deficiency in diets could require metabolic compensation detrimental to development.Adult T. minutum arising from eggs of Manduca sexta, Choristoneura fumiferana, and Sitotroga cerealella are similar in amino acid composition to each other and, in general, to their hosts. Variability appears greater in hosts than in adult wasp composition, suggesting some interconversion of host amino acids to accommodate inflexible nutritional requirements of T. minutum.In the three host species tested, free amino acids constituted 15.8–19.3% by weight of the amino acid in egg contents. In M. sexta eggs, glycine, serine and alanine together make up 28.4% by weight of the total free amino acid, a much higher proportion than in many published diets. The four free amino acids (isoleucine, leucine, phenylalanine and histidine) reported to be oviposition stimulants in experiments on encapsulated diets are present in sufficient concentrations to induce oviposition in the host species tested and in R. prolixus. S. cerealella egg contents having approximately 1.8 g amino acid, yield one or rarely two adult T. minutum (1g amino acid/insect). In contrast, M. sexta eggs with 94 g amino acid each yield an average of 10–12 adults (8.2g amino acid/insect). This suggests that small hosts are allocated few eggs which can only develop into small adults because of nutrient supply (parasitoid size in metabolically restricted), whereas much larger hosts are allocated proportionately fewer eggs than the former resulting in larger, and presumably more viable and fecund, adults (parasitoid size is established behaviourally).     

Effects of auxins,cytokinins, carbohydrates and amino acids on somatic embryogenesis induction from shoot apices of pea

Studies were conducted to test the effects of various auxins, cytokinins, carbohydrates and amino acids on somatic embryogenesis from shoot apices of pea (Pisum sativum L.) cultured on a sole medium. Picloram (4.5 M) and 4-chlorophenoxyacetic acid (45 M) were the most effective auxins. Addition of cytokinins (benzyladenine, zeatin, kinetin) to auxin-containing medium reduced embryo production. Amino acids (glutamine, alanine, proline) did not improve somatic embryogenesis. Carbohydrate seemed to be a critical factor. Embryogenic efficiency and embryo development were promoted by high carbohydrate concentration. The best results were obtained with fructose (252–504 mM); the number of somatic embryos per cultured explant was 3- to 4-fold higher compared to the control (84 mM sucrose). From these results, an optimized induction medium is proposed.Abbreviations BA benzyladenine - 4-CPA 4-chlorophenoxyacetic acid - 2,4-d 2,4-dichlorophenoxyacetic acid - NAA 1-naphthaleneacetic acid - 2,4,5-T 2,4,5-trichlorophenoxyacetic acid - MS Murashige & Skoog - EE embryogenic explants - G globular somatic embryos     

A rapid method for isolation of purified,physiologically active chloroplasts,used to study the intracellular distribution of amino acids in pea leaves

A procedure is described for the rapid (<5 min) isolation of purified, physiologically active chloroplasts from Pisum sativum L. Mitochondrial and microbody contamination is substantially reduced and broken chloroplasts are excluded by washing through a layer containing a treated silica sol. On average the preparations contain 93% intact chloroplasts and show high rates of ¹⁴CO₂ fixation and CO₂-dependent O₂ evolution (over 100 mol/mg chlorophyll(chl)/h); they are also able to carry out light-driven incorporation of leucine into protein (4 nmol/mg chl/h). The amino-acid contents of chloroplasts prepared from leaves and from leaf protoplasts have been determined. Asparagine is the most abundant amino acid in the pea chloroplast (>240 nmol/mg chl), even thought it is proportionately lower in the chloroplast relative to the rest of the cell. The chloroplasts contain about 20% of many of the amino acids of the cell, but for individual amino acids the percentage in the chloroplast ranges from 8 to 40% of the cell total. Glutamic acid, glutamine and aspartic acid are enriched in the chloroplasts, while asparagine, homoserine and -(isoxazolin-5-one-2-yl)-alanine are relatively lower. Leakage of amino acids from the chloroplast during preparation or repeated washing was ca. 20%. Some differences exist between the amino-acid composition of chloroplasts isolated from intact leaves and from protoplasts. In particular, -aminobutyric acid accumulates to high levels, while homoserine and glutamic acid decrease, during protoplast formation and breakage.     

Use of the egg parasiteEdovum puttleri [Hym.: Eulophidae] in an IPM system developed for Colorado potato beetle [Col.: Chrysomelidae] control on potatoes,Beltsville, Maryland

Edovum puttleri Grissell in conjunction with the fungal pathogenBeauveria bassiana (Balsamo) Vuillimen, a β-exotoxin ofBacillus thuringiensis varthuringiensis Berliner, and the insect growth regulator triflumuron (Alsystin 4F) were evaluated in a pest management system to control Colorado potato beetle,Leptinotarsa decemlineata (Say). Soil treatments ofB. bassiana had no significant impact on emerging Colorado potato beetle adults. Foliar applications of the β-exotoxin and triflumuron significantly reduced 1 ^st larval generation. Releases ofE. puttleri resulted in 56 % egg mass parasitization, significant reduction of 2 ^nd generation larvae, and significantly higher potato yields.Leptinotarsa texana (Schaeffer) was successfully used as an alternate host for production ofE. puttleri.      

Effects of a vesicular-arbuscular mycorrhizal fungus and other soil microorganisms on growth,mineral nutrient acquisition and root exudation of soil-grown maize plants

Maize (Zea mays L. cv. Alize) plants were grown in a calcareous soil in pots divided by 30-m nylon nets into three compartments, the central one for root growth and the outer ones for hyphal growth. Sterle soil was inoculated with either (1) rhizosphere microorganisms other than vesicular-arbuscular mycorrhizal (VAM) fungi, (2) rhizosphere microorganisms together with a VAM fungus [Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappel], or (3) with a gamma-irradiated inoculum as control. Plants were grown under controlled-climate conditions and harvested after 3 or 6 weeks. VAM plants had higher shootroot ratios than non-VAM plants. After 6 weeks, the concentrations of P, Zn and Cu in roots and shoots had significantly increased with VAM colonization, whereas Mn concentrations had significantly decreased. Root exudates were collected on agar sheets placed on the interface between root and hyphal compartments. Six-week-old VAM and non-VAM plants had similar root exudate compositions of 72–73% reducing sugars, 17–18% phenolics, 7% organic acids and 3% amino acids. In another experiment in which root exudates were collected on agar sheets with or without antibiotics, the amounts of amino acids and carbohydrates recovered were similar in VAM and non-VAM plants. However, threeto sixfold higher amounts of carbohydrates, amino acids and phenolics were recovered when antibiotics were added to the agar sheets. Thus, the high microbial activity in the rhizosphere and on the rhizoplane limits the exudates recovered from roots.     

Influence of carbohydrates and polyols on l-lactic acid production and fatty acid formation by Rhizopus arrhizus

Growth and l-lactic acid production on 24 different carbohydrates and polyols (glycerol, mannitol and sorbitol) by Rhizopus arrhizus CCM 8109 were determined. The d- but not the l-forms of xylose, fructose, galactose, mannose, glucose, cellobiose, maltose and sucrose and partially hydrolysed starch were converted to l-lactic acid. Changes in lipid formation and fatty acid composition were detected in biomass grown on the different sugars. In the presence of polyols, growth and considerable production of lipids were observed with little or no lactate production. Invertase was mainly associated with the mycelium during growth on sucrose, whereas glucoamylase and -amylase were produced extracellularly during growth on starch.The authors are with the Department of Biochemical Technology, Faculty of Chemical Technology, Slovak Polytechnical University, Radlinského 9, SK-812 37 Bratislava, Slovak Republic     

The amino acid transport systems of the autotrophically grown green alga Chlorella

The kinetic analysis of l-amino acid uptake by the green alga Chlorella revealed at least seven different uptake systems to be present in cells grown autotrophically with nitrate as nitrogen source. There is a ‘general system’ which transports most neutral and acidic amino acids, a system for short-chain neutral amino acids including proline, a system for basic amino acids including histidine, a special system for acidic amino acids, and specific systems for methionine, glutamine and threonine. The ‘general system’ is possibly the same as that which can be stimulated by incubation of cells in glucose plus ammonium (Sauer, N. (1984) Planta 161, 425–431). The incubation of Chlorella in glucose induces the increased synthesis of six amino acid uptake systems, namely the above-mentioned system for short-chain neutral amino acids, a threonine system, a methionine system, and a glutamine system. These results indicate that the uptake of l-amino acids by the green alga Chlorella is as complex as in other free-living organisms such as bacteria or yeast. The small number of amino acid uptake systems found in cells of higher plants, i.e. two or three, seems therefore to be a consequence of integration of the cells in a tissue supplying a relatively constant environment, and not a consequence of autotrophic growth on mineral carbon and mineral nitrogen.     

Purification and regulation of glutamine synthetase in a collagenolytic Vibrio alginolyticus strain

Glutamine synthetase (EC 6.3.1.2) has been purified from a collagenolytic Vibrio alginolyticus strain. The apparent molecular weight of the glutamine synthetase subunit was approximately 62,000. This indicates a particle weight for the undissociated enzyme of 744,000, assuming the enzyme is the typical dodecamer. The glutamine synthetase enzyme had a sedimentation coefficient of 25.9 S and seems to be regulated by a denylylation and deadenylylation. The pH profiles assayed by the -glutamyltransferase method were similar for NH₄-shocked and unshocked cell extracts and isoactivity point was not obtained from these eurves. The optimum pH for purified and crude cell extracts was 7.9. Cell-free glutamine synthetase was inhibited by some amino acids and AMP. The transferase activity of glutamine synthetase from mid-exponential phase cells varied greatly depending on the sources of nitrogen or carbon in the growth medium. Glutamine synthetase level was regulated by nitrogen catabolite repression by (NH₄)₂SO₄ and glutamine, but cells grown, in the presence of proline, leucine, isoleucine, tryptophan, histidine, glutamic acid, glycine and arginine had enhanced levels of transferase activity. Glutamine synthetase was not subject to glucose, sucrose, fructose, glycerol or maltose catabolite repression and these sugars had the opposite effect and markedly enhanced glutamine synthetase activity.Abbreviations GS glutamine synthetase - SMM succinate minimal medium - ASMM ammonium/succinate minimal medium - GT -glutamyl transferase - SVP snake venom phosphodiesterase