Free Amino Acid Fraction Research Articles

Elaborating the Atmospheric Transformation of Combined and Free Amino Acids From the Perspective of Observational Studies

AbstractProteinaceous matter (PrM) is a substantial component of bioaerosols. Although numerous studies have examined the characteristics and sources of PrM in the atmosphere, its interactions with atmospheric oxidants remain uncertain. A 1‐year observation of PrM characteristics in PM2.5 was performed in both urban Nanchang (eastern China) and suburban Guiyang (southwestern China), respectively. Glycine was the dominant free amino acid (FAA) species in urban Nanchang. In contrast, proline dominated both total free amino acids (FAAs) and total combined amino acids (CAAs) in suburban Guiyang. We found that oxidative degradation can significantly promote the release of FAAs, especially glycine, from CAAs in Nanchang. The controlled experiment on protein oxidation by hydroxyl radical suggested that the contribution of free glycine to the total FAA fraction tended to increase during the oxidative degradation of CAAs, supporting the predominance of glycine in FAAs in Nanchang and most previous observations. The composition of FAAs was mainly influenced by primary sources in suburban Guiyang with weak atmospheric degradation of PrM. These results suggest that the degradation of aerosol PrM by atmospheric oxidants can be responsible for the difference in FAA composition between the biosphere and the atmosphere, and also imply that the oxidative degradation of aerosol PrM may be a potential source of secondary organic nitrogen compounds in aerosols. Thus, this study can improve the current understanding of the composition characteristics of PrM in the biosphere and the atmosphere, as well as the liquid phase reactions of proteinaceous compounds with atmospheric oxidants.

Effect of Marinating Temperature of Atlantic Herring on Meat Ripening, Peptide Fractions Proportion, and Antioxidant Activity of Meat and Brine

The temperature has a significant effect on cathepsin activity, but the effect of temperature on the ripening of marinades, and the formation of protein hydrolysis products, is less studied than other technological factors. The results of this study showed that herring marinated at 2 °C showed a higher mass yield, but lower non-protein nitrogen (NPN), peptides, and free amino acid fraction content, than after marinating at 7 and 12 °C. The higher temperature increased the free amino acid content the most, and decreased the hardness, as measured via sensory assessment, of the marinated meat. This was confirmed by the hardness measurement in the texture profile analysis. The highest activity of cathepsins D and B in the meat was found at 7 °C, while cathepsin L was found at 2 °C. Increasing the temperature by 10 °C increased the diffusion/loss of nitrogenous substances from the meat to the brine by 36%. The meat and brine showed high antioxidant activity, which depended on the marinating temperature, and originated mainly from the 5–10 or <5 kDa fraction. The meat had a higher ABTS (2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonate) activity than the brine, opposite to the DPPH (2,2-diphenyl-1-picrylhydrazyl radical) activity, while the FRAP (Ferric Reducing Antioxidant Power) capacity was similar for meat and brine. The fractionation of the meat and brine extracts increased the antioxidant potential of FRAP and ABTS only for the brine. The most hydrophobic peptides were released during marinating at 7 °C. The meat and brine were dominated by 2–4 kDa peptides, followed by 4–6 and 0.5–2 kDa. The higher temperature favored a higher proportion of <4 kDa than >4 kDa peptides in the brine.

Evidence of gastrointestinal sensing and gut-brain communication in rainbow trout (Oncorhynchus mykiss) in response to the aqueous extract of fishmeal and its free amino acid fraction

Using rainbow trout (Oncorhynchus mykiss) as a model, we aimed to obtain information about the gastrointestinal tract (GIT) amino acid sensing capacity and hormone production along regions of the GIT, in response to proline (Pro), to a solution of free amino acids (FAA) mimicking the composition of a fishmeal (FM) aqueous extract (FM-FAA), or to the whole FM aqueous extract (FM-AQE). In addition, we evaluated central responses (in hypothalamus) in mechanisms regulating food intake, 2 h following intragastric administration of these treatments. The presence of Pro in the GIT elicited changes in amino acid sensing systems and in the production of GIT hormones, especially in the more proximal regions in parallel with an anorectic response in hypothalamus. The intragastric administration of FM-AQE induced increased production of the anorectic hormones peptide tyrosine-tyrosine (PYY) and cholecystokinin (CCK) that occurred 20 min post-treatment in the proximal and middle intestine of this treatment. These changes occurred in parallel with an anorectic response in the hypothalamus 2 h post-treatment. The treatment with FM-FAA elicited a comparable anorectic response in the hypothalamus at 2 h post-treatment, which was associated however with a more complex response in the GIT. This included a comparable increased production of the anorectic hormones PYY and CCK in the proximal and middle intestine, but also a decreased production of the orexigenic hormone ghrelin (GHRL) in the stomach, 20 min after FM-FAA administration. These effects were also accompanied by some changes in parameters related to amino acid sensing systems mediated by receptors, which were not observed in the FM-AQE treatment. Overall, results indicate that all treatments elicited a response in elements of gut sensing mechanisms and gut-brain axis, despite important differences in the specific genes (likely having different substrate specificities), GIT areas and times in which responses were observed.

A new approach to recycling cephalosporin fermentation residue into plant biostimulants

Cephalosporin fermentation residue (CFR), a byproduct of the pharmaceutical industry, mainly contains the mycelial biomass and unutilized culture medium, which can be reused as a high-quality protein source. This study first reports the recycling CFR into plant biostimulants using partial acid hydrolysis. Temperature, reaction time and ratio of hydrochloric acid/dry matter (H/S) were optimized for yielding both free amino acid and low molecular weight fraction based on response surface methodology. The crude protein concentration of CFR is 55%, with glutamic acid being the dominant amino acid (12.5%). Two favorable hydrolysis conditions were obtained: (1) 140 °C, 10.7 h, 17 H/S for maximizing the amino acid yield of 45.5 g/100 g CFR dw and (2) 100 °C, 10.7 h, 19 H/S for maximizing the low molecular weight fraction of 28.2%. The CFR-derived biostimulants obtained from two optimum conditions possessed two biostimulant modes of action: plant growth promotors/inhibitors and stress alleviators. However, they showed the differences in aminograms and profiles of low molecular weight compounds. Neither residual cephalosporin C nor its byproduct was detected in the CFR-derived biostimulants, suggesting that partial acid hydrolysis appears capable of recycling CFR into plant biostimulant safely.

Production of protected amino acids using the reaction between hydroxycarboxylic acids and amino acids as well as binding on the bentonite

Abstract We have developed methods for the production of protected methionine and protected lysine, making use of the reaction between citric acid and malic acid as well as methionine and lysine, on the one hand, and of the interaction between swollen bentonite and the two amino acids, on the other hand. Our in vivo and in vitro experiments have demonstrated that one part of the amino acids transformed during the reaction, while another part bound on the bentonite’s surface to a significant degree. Assisted by the reaction between hydroxycarboxylic acids and amino acids, we achieved a protection of about 75% for methionine and 60% for lysine, that is, 25% of the methionine and 40% of the lysine appeared in the free amino acid fraction. The swollen bentonite bound 75% of the added methionine and 60% of the added lysine. Our chemical analyses have demonstrated that through the time–temperature combinations applied by us the methionine and lysine do not undergo significant degradation and can be fully released from the protected form. Further, our in vitro experiments using rumen fluid from fistulated cattle showed that during the average retention time of the fodder in the rumen the protected amino acids will resist microbial enzymes and maintain their protected status during their presence in the rumen.

Amino acid composition of the bushcricket spermatophore and the function of courtship feeding: Variable composition suggests a dynamic role of the nuptial gift

Nuptial gifts are packages of non-gametic material transferred by males to females at mating. These gifts are common in bushcrickets, where males produce a complex spermatophore consisting in a sperm-containing ampulla and an edible sperm-free spermatophylax. Two non-mutually exclusive hypotheses have been suggested to explain the function of the spermatophylax: the paternal investment hypothesis proposes that it represents a male nutritional investment in offspring; the mating effort hypothesis proposes that the spermatophylax maximizes the male's sperm transfer. Because gift production may represent significant energy expenditure, males are expected to adjust their investment relative to the perceived quality of the female. In this study, we first examined the free amino acid composition and protein-bound amino acid composition of the nuptial gift in the bushcricket, Ephippiger diurnus (Orthoptera: Tettigoniidae). Second, we investigated whether this composition was altered according to female age and body weight. Our study represents the first investigation of both free and protein-bound amino acid fractions of a bushcricket spermatophylax. We found that composition of the nuptial gift varied both qualitatively and quantitatively with respect to traits of the receiving female: older females received larger amounts of protein-bound amino acids (both essential and non-essential), less water and less free glycine. This result suggests that gift composition is highly labile in E. diurnus, and we propose that gift allocation might represent a form of cryptic male mate choice, allowing males to maximize their chances of paternity according to the risk of sperm competition that is associated with mate quality.

Effect of extracts from heshiko, a fermented mackerel product, on cholesterol metabolism in Wistar rats

Heshiko extract was separated into peptide and amino acid fractions by ion-exchange column chromatography. Heshiko extract and these fractions were administered to rats in a diet enriched with lipid and cholesterol for 30 days. In the heshiko extract group, increase of triglyceride, total cholesterol, and low-density lipoprotein (LDL)-cholesterol levels in plasma and accumulation of total lipids in the liver were suppressed, while amounts of both lipid and cholesterol excreted to feces were increased. Administration of heshiko extract tended to increase fecal bile acids and promoted the activity of cholesterol 7α-hydroxylase, the rate-limiting enzyme in the synthesis of bile acid from cholesterol in the liver. However, activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate-limiting enzyme in the cholesterol synthesis system in the liver, decreased due to regulation by the feedback of lipid transportation from diet to the liver. The same effect was observed in the peptide and free amino acid fraction groups. These data suggest that both excretion of cholesterol and bile acid to feces and promotion of cholesterol 7α-hydroxylase activity are related to the hypocholesterolemic effects of heshiko extract and that both peptides and amino acids contribute to that effect.

Biochemical and technical observations supporting the use of copepods as live feed organisms in marine larviculture

The use of live prey is still necessary for a large number of raised fish species. Small sized rotifers are usually used as live preys during the first days of feeding in small mouth fish. An alternative to this is the use of copepods as prey for first feeding. In this study, the sizes, weight and biochemical contents of two copepods and one rotifer species raised on similar algal food conditions were compared. Rotifers contained a higher proportion of essential amino acids in the free amino acid (FAA) fraction (43%) than copepods (30–32%). However, rotifers had lower levels of important fatty acids like DHA (7% compared with 23–32% in copepods) and their DHA/EPA ratio was lower than that in copepods (0.54 compared with 1.35–1.63 in copepods). The FAA pattern of the preys tended to be species-specific and its implications from an aquaculture point of view is discussed. In contrast, the-protein bound amino acids tended to be very conservative among the studied organisms. The second part of the work is focused on ‘the price’ of hatching in Acartia tonsa eggs before or after cold storage at 3°C. The fatty acid contents in A. tonsa tended to decrease with the storage time. It also decreased with hatching of the nauplii, but its proportion compared with the dry weight remained constant.

Amino acids in dew – origin and seasonal variation

At two sites in the Armenhof district, 10 km east of Fulda, Germany, dew samples were collected from June 1996 to June 1997 and investigated for free and protein-bound amino acids. On account of the high pollen content, at the beginning of June 1996 and in May 1997 total amino acid concentrations were 53–390 μmol l −1, in one sample 922 μmol l −1. At other times the concentration in dew was 8–164 μmol l −1. On 4 and 5 June 1996 the diluted free amino acid fraction (DFAA) of the total hydrolysed amino acids (THAA) at both sites amounted to 35–44% and was predominantly arginine, proline and glutamine/glutamate. Likewise on 11 March 1997 the fraction of DFAA was found to be 39.5% with extremely high arginine and proline fractions. At other times the DFAA-fraction was in the range 14–26%. From July 1996 to June 1997 the amino acid concentrations in the vapours rising from a meadow were also measured and it ranged from 8 to 51 μmol l −1. From July to October 1996 the amino acid composition in the hydrolysates of dew samples and meadow vapours collected overnight were almost identical. The DFAA fraction in the condensation water collected overnight from the meadow varied from 18 to 40%. From 4 to 6 June 1996, on 11 and 13 March 1997 and in the period 16–20 May 1997, the amino acid distribution in dew showed much variation. The percentage fraction of arginine and proline in the hydrolysate increased greatly, whereas that of glycine and serine decreased. The large increase in proline and arginine in hydrolysate is attributable solely to the large amounts of free arginine and proline. This effect occurred in both 1996 and 1997 over several days at both sites at any one time and therefore appears confirmed.

Compartmental modeling of postprandial dietary nitrogen distribution in humans.

A linear 11-compartment model was developed to describe and simulate the postprandial distribution of dietary nitrogen. The values of its 15 constant diffusion coefficients were estimated from the experimental measurement of (15)N nitrogen kinetics in the intestine, blood, and urine after the oral administration of (15)N-labeled milk protein in humans. Model structure development, parameter estimation, and sensibility analysis were achieved using SAAM II and SIMUSOLV softwares. The model was validated at each stage of its development by testing successively its a priori and a posteriori identifiability. The model predicted that, 8 h after a meal, the dietary nitrogen retained in the body comprised 28% free amino acids and 72% protein, approximately 30% being recovered in the splanchnic bed vs. 70% in the peripheral area. Twelve hours after the meal, these values had decreased to 18 and 23% for the free amino acid fraction and splanchnic nitrogen, respectively. Such a model constitutes a useful, explanatory tool to describe the processes involved in the metabolic utilization of dietary proteins.

Free amino acids and proteolysis involved in ‘salchichon’ processing

Changes in free amino acid and nitrogen fraction contents involved in salchichón manufactured by industrial processing at different times of curing process were analysed. An increase in the free amino acid concentration and non protein fraction was observed during the curing process, specially between the fermentation stage and the second week of drying while soluble protein nitrogen decreased. The predominant amino acids in the initial mix of salchichon were Glutamic acid, Cysteine, Carnosine, Alanine and Taurine summing up the 73.7% of the total. During the last two weeks of drying, the concentration of some of the free amino acids went on increasing (Aspartic acid, Glutamic acid, Serine, Asparragine, Glycine, Taurine, Threonine, Alanine, Carnosine, Tryptophan and Lysine) but some others decreased significantly (Proline, Tyrosine, Valine, Methionine, Cysteine, Isoleucine and Leucine). The curing stage of salchichon might be estimated approximately based on the concentration of Aspartic acid, Glutamic acid, Serine, Glycine, Asparragine, Threonine and the total free amino acid content amino acids. The majority of amino acids that showed the greatest concentration in the final product were recorded as having `bitter' flavour characteristics.

Waterlogging affects nitrogen transport in the xylem of soybean

Transfer of nodulated and non-nodulated plants grown in vermiculite to hydroponic culture without soil was used to study waterlogging and nitrogen transport in the xylem of soybean. Non-aeration, aeration or aeration with nitrogen gas were used to obtain different levels of oxygen in the culture solutions. Ureides, the principal form of nitrogen transport in nodulated plants, were considerably reduced in waterlogged plants or after transfer to water-culture, especially when not aerated or aerated with nitrogen gas. Aeration of the water-culture following a period of non-aeration allowed some recovery of ureides, as did the return of plants to drained vermiculite. Although smaller changes in the total amino acid fraction were observed for the different treatments, marked changes occurred in the composition depending on the treatment imposed. A high proportion of asparagine and low glutamine characterised non-nodulated plants grown on nitrate, or nodulated plants subsequently fed nitrate. A higher level of glutamine and lower level of asparagine characterised nodulated plants dependent on nitrogen fixation. High levels of aspartic acid characterised plants transferred to water-culture with aeration, especially in N-deficient solution, while alanine and serine were very prominent in non-aerated or hypoxic water-culture. These changes also occurred in non-nodulated plants and plants kept in vermiculite in a flooded condition. Some of the changes in transport were accompanied by similar changes in the free amino acid fraction of the roots. It is suggested that an alteration in asparagine metabolism may underlie the changes in amino acid transport in the xylem associated with waterlogging.

Simultaneous addition of Palatase M and Protease P to a dry fermented sausage (Chorizo de Pamplona) elaboration: Effect over peptidic and Lipid fractions

The effect of the simultaneous addition of a lipase (Palatase M 200L Novo Nordisk A/S) and a protease (Protease P 31.000 Solvay Enzymes GMBH&CO.KG) to the manufacture of a Spanish dry fermented sausage (Chorizo de Pamplona) was studied. In relation to the free aminoacid fraction, significative increases in Glu, His, Lys, Ser, Ala, Pro, Val, Met, Ile, Leu and Phe were found. Smaller differences were observed in the aminoacids obtained from peptides. The addition of the lipase caused significant increases in palmitic, oleic and linolenic acids. Despite the observed changes, no differences were found in the sensory quality compared with the control, except for a slight softening.

Comparison of isoleucine epimerization and leaching potential in the molluskan genera Astarte, Macoma, and Mya

Amino acid racemization geochronology is widely applied to provide relative age control for carbonate fossils, however, there are significant chemical differences between genera which affect diagenetic reactions in proteins such as hydrolysis and racemization. In order to evaluate intergeneric influences on isoleucine epimerization, laboratory heating experiments were undertaken to compare the rate of epimerization of L-isoleucine to D-alloisoleucine and the potential for leaching of amino acids in three molluskan genera: Astarte, Macoma, and Mya. Shell fragments from these genera were heated for up to 816 h at 100°C to simulate aging. After 96 h of heating, the three genera experienced similar degrees of epimerization in the total acid hydrolysate, but with additional heating, Astarte and Macoma epimerized more extensively than Mya. In the free amino acid fraction, the relative rates of epimerization were reversed: Mya shows the fastest apparent rate and Astarte the slowest.All three genera lost amino acids from both the free and bound fractions by leaching, but more significantly, alloisoleucine leached proportionately much faster than isoleucine. If leaching of amino acids under natural conditions continues after significant alloisoleucine is produced, then the preferential loss of alloisoleucine over isoleucine will result in lowering of the alloisoleucine/isoleucine ratio and, therefore, lead to significant underestimation of ages. An important implication for all studies utilizing amino acid racemization geochronology is that even coeval shells of the same genus may give different alle/Ile values if different individual shells experienced different burial conditions and degrees of leaching.

Free Amino Acid and Storage Protein Composition of Soybean Fruit Explants and Isolated Cotyledons Cultured with and without Methionine

Thein vitroculture of immature soybean cotyledons (in direct contact with the medium) and immature fruit explants (stem dipping into the medium) on a defined medium containing glutamine and sulphate as sole sources of N and S for 7 d led to rates of growth and reserve protein accumulation close to, or greater than, those occurringin situ. Supplementation of the medium with 8.4 mMmethionine had little effect on growth and protein accumulation of the cotyledons in the explant system, but did result in significant increases in the isolated cotyledon system. Methionine suppressed the synthesis of the 7S β-subunit in both systems. The free amino pool of the cotyledons increased more than three-fold when methionine was present in the explant medium. In the isolated cotyledon system, the basal medium alone caused a large increase (over 30-fold) in the free amino acid fraction, but methionine resulted in an even greater increase (over 50-fold). In both systems the expansion involved a very large increase in the methionine pool, but many other amino acids also showed large increases. Specific effects of methionine on individual amino acids were more clear in the explant system, where its presence resulted in marked increases in serine, alanine and asparagine. The data show that an abnormal situation arises on feeding with methionine, a fact to be considered before attributing effects on growth and protein synthesis directly to methionine.

Addition of a Neutral Proteinase fromBacillussubtilis(Neutrase) Together with a Starter to a Dry Fermented Sausage Elaboration and Its Effect on the Amino Acid Profiles and the Flavor Development

Amino acid profiles from the peptide and free amino acid fractions were studied during the ripening of a traditional fermented sausage (chorizo) when a proteinase from Bacillus subtilis (Neutrase) was added. Total increase in free amino acids (FAA) was similar in both products, but its evolution was different. A slight decrease of some amino acids (Asp, Thr, Ala, Met, and Lys) was found in the product with Neutrase between the third and ninth days against the continuous increment observed in the control along the ripening. Total increase of the peptide fraction amino acids during the elaboration was more intense with enzyme. Both products showed a significant decrease of this fraction in the last week, which was higher in the product with Neutrase, which showed the highest increase in the FAA at that period. Sensory analysis showed a slight improvement on the overall acceptability significantly correlated with some flavor parameters. Keywords: Fermented sausages; exogenous proteases; amino acids profiles

Marginal dietary protein restriction reduced nonprotein nitrogen, but not protein nitrogen, components of human milk.

This study was designed to determine whether marginal dietary protein intakes of lactating women alter their milk production and composition. The study followed the observation that marginal dietary protein intakes lead to significantly negative nitrogen balances in these women. Twenty-four healthy, mature lactating women were divided evenly into three groups on the basis of postpartum times; 1, 5, or 12 months. Each woman was given a controlled protein diet of either 1.5 (HP) or 1.0 (MP) g/kg body weight/day for 7 to 10 days. Milk production was measured for 72 hours by test weighing the infant before and after feeding. Milk samples from alternate breasts were collected for 24 hours, pooled, and analyzed for their protein nitrogen, nonprotein nitrogen, free and protein-bound amino acid, and lactoferrin concentrations. Reduced dietary protein intakes were associated with a decrease (p < 0.05) in the nonprotein nitrogen and total free amino acid fractions of milk. Although urea was unaffected, the concentrations of milk free leucine, phenylalanine, histidine, and ornithine were lower (p < 0.05) in the MP than in the HP group, while the output of leucine and histidine tended to be lower in the MP group. The amount of milk produced, as well as the amounts of protein nitrogen, protein-bound amino acid, and lactoferrin and their concentrations were unaffected by a reduction of dietary protein. Maternal milk production and the protein nitrogen, but not the nonprotein nitrogen, fraction of human milk were relatively well-preserved in the presence of a short-term, marginal reduction of dietary protein.

Changes in free amino acids of hake (Merluccius merluccius L.) muscle during frozen storage/Cambios producidos en los aminoácidos libres del músculo de merluza (Merluccius merluccius L.) durante su conservación en estado congelado

The effect of storage at subzero temperatures (-5°C, -12°C, and -20°C) on hake ( Merluccius merluccius L.) muscle free-amino acid fraction was evaluated. A significant increase in free aspartic acid, serine, threonine, arginine, β-alanine, tyrosine, methionine, valine, phenylalanine, isoleucine, leucine, and lysine was found at -5°C, whereas at -12°C, a significant decrease in free glutamic acid, glycine, methyl-histidine, β-alanine, taurine, alanine, and leucine was the most noticeable. No changes in the free amino acid fraction were observed at -20°C. Activity of different kind of enzymes, aminopeptidases, aminoacid deaminases, and decarboxylases might be involved in the changes observed at -5°C and -12°C.

Main routes of plasma lactate carbon disposal in the midgestation fetal lamb.

The turnover rates of plasma lactate, normalized for O2 consumption rate, are higher in the fetus than in the adult. This occurs despite very low rates of fetal gluconeogenesis which preclude the recycling of lactate carbon into glucose. In an effort to establish the main routes of disposal of fetal plasma lactate, 12 midgestation ovine fetuses (age 74 +/- 1 days) were infused intravenously at constant rate with L-[U-14C]lactate for a 4-hour period. At the end of the infusion, the amounts of 14C retained by the fetus and by the placenta, and the distribution of the retained 14C in free and protein-bound amino acids and in lipids were measured. Of the total 14C infused, 17.0 +/- 1.4% was recovered in the placenta, 4.0 +/- 0.3% in the fetal liver, and 15.0 +/- 0.8% in the extrahepatic fetal tissues. Of the retained radioactive carbon, 45-57% was recovered in the free and protein-bound amino acid fractions and 11-17% in the lipid fractions. Approximately 90% of the 14C in the free amino acid fractions was present as glutamate/glutamine, serine, glycine, and alanine carbon. In conjunction with data on fetal CO2 production from lactate carbon, these results demonstrate that the main routes of fetal lactate disposal are oxidation and synthesis of nonessential amino acids and lipids.

Phytoplankton extracellular release and bacterial growth: dependence on the inorganic N: P ratio

Batch cultures of Chaetoceros affinis grown under nitrogen- (N:P = 5) and phosphorus- (N:P = 100) limited conditions exhibited 30 and 100% higher rates of photosynthetic extracellular release (PER), respectively, than C affims grown under balanced nutrient conditions (N.P = 16). Inoculations of natural bacterial assemblages to PER derived from phytoplankton grown under these different nutrient regimes exhibited highest potential bacterial growth yields (- 46 %) on PER derived from balanced growth. Analysis of the dissolved monomeric (MCHO) and polymeric (PCHO) carbo- hydrate pool and of the dissolved free amino acid (DFAA) fraction of the PER indicated significantly higher specific release rates of these components for phytoplankton grown under P limitation Based on the fluctuation of the MCHO, PCHO and DFAA pool in the batch cultures and on bacterial extra- cellular enzymatic activity (EEA) and bacterial growth yield we have evidence that under P-limited conditions bacteria are not taking up the available carbon efficiently. Bacteria growing on PER derived from N-lmted conditions exhibited high bacterial a- and p-glucosidase activity, while under P limta- tion low EEA was detectable. Extrapolating our results to the severely P-limited summer conditions of the Northern Adriatic Sea, we might conclude that P limitation provokes elevated PER m exponentially growing phytoplankton which is not utilized efficiently by the natural bacterial consortia. This would allow the PER to coagulate and eventually form mucilage.