Dynamics of amino acids in the conditioning film developed on glass panels immersed in the surface seawaters of Dona Paula Bay

The conditioning film developed on glass panels immersed in surface seawater over a period of 24?h was analysed for total organic carbon (OC), total organic nitrogen (ON), and total hydrolyzable amino acid (THAA) concentrations and composition. The concentrations of C and N and THAA increased, whereas the C/N ratio decreased over the period of immersion. The amino acid-C and N accounted for 3.7?–?6.7% and 10.3?–?65.3% of OC and ON, respectively. The relative contribution of glycine plus threonine and serine to the total amino acids decreased while that of valine, phenylalanine, isoleucine and leucine increased over the period of immersion. Principal component analysis (PCA) based on mole% amino acid composition showed that the degradation indices (DI) for the conditioning film organic matter increased over the period of immersion. A high C/N ratio, a low %THAA-C, % THAA-N and DI values and the abundance of glycine plus threonine and serine in the conditioning film organic matter during the first few hours following immersion imply that the adsorbed organic matter was mostly derived from degraded organic matter.     

Analysis of microfouling products formed on metallic surfaces exposed in a marine environment

Mild steel (MS), stainless steel (SS) and copper (Cu) test panels were immersed in the surface water of Dona Paula Bay over a period of 15 d. During the immersion period data on the hydrography, nutrients and suspended matter were also collected. The suspended matter and fouling products on the MS, SS and Cu panels were analysed for organic carbon (OC), organic nitrogen (ON), chlorophyll a (chl a), protein and carbohydrate concentration and composition, and the dry weight (DW) was recorded. Compared to suspended matter, the chemical and biochemical components of the fouling products showed strong temporal and substratum related differences. The microfouling biomass (as DW, OC, ON, chl a and protein) on all the test panels generally increased over the period of immersion. Carbohydrates were more abundant in the suspended matter whereas fouling products were enriched in proteins. The contribution of protein-carbon to the total carbon increased over the period of immersion for the microfouling products on MS and SS whilst it did not show a consistent trend on Cu. Whereas, the carbohydrate-carbon contribution to the total carbon increased for the fouling products on MS, it did not exhibit a particular pattern on SS or Cu over the period of immersion. Capillary gas chromatographic analysis showed the presence of glucose, galactose, mannose, arabinose, xylose fucose and ribose in both the fouling products and suspended matter. However, there were differences in the relative distribution of these monosaccharides in the suspended matter and the fouling products. Glucose was the most abundant monosaccharide, which showed strong temporal variations in suspended matter. In contrast, the wt % concentrations of individual monosaccharides showed large temporal differences for the fouling products, which were strongly influenced by the period of immersion and the type of test substratum. Glucose and fucose were relatively more abundant in the fouling products on SS and Cu, whilst glucose was the most abundant monosaccharide on MS. The monosaccharide and chemical composition data suggest strong temporal changes in the composition of the fouling products.     

Analysis of Microfouling Products Formed on Metallic Surfaces Exposed in a Marine Environment

Mild steel (MS), stainless steel (SS) and copper (Cu) test panels were immersed in the surface water of Dona Paula Bay over a period of 15 d. During the immersion period data on the hydrography, nutrients and suspended matter were also collected. The suspended matter and fouling products on the MS, SS and Cu panels were analysed for organic carbon (OC), organic nitrogen (ON), chlorophyll a (chl a), protein and carbohydrate concentration and composition, and the dry weight (DW) was recorded. Compared to suspended matter, the chemical and biochemical components of the fouling products showed strong temporal and substratum related differences. The microfouling biomass (as DW, OC, ON, chl a and protein) on all the test panels generally increased over the period of immersion. Carbohydrates were more abundant in the suspended matter whereas fouling products were enriched in proteins. The contribution of protein-carbon to the total carbon increased over the period of immersion for the microfouling products on MS and SS whilst it did not show a consistent trend on Cu. Whereas, the carbohydrate-carbon contribution to the total carbon increased for the fouling products on MS, it did not exhibit a particular pattern on SS or Cu over the period of immersion. Capillary gas chromatographic analysis showed the presence of glucose, galactose, mannose, arabinose, xylose, fucose and ribose in both the fouling products and suspended matter. However, there were differences in the relative distribution of these monosaccharides in the suspended matter and the fouling products. Glucose was the most abundant monosaccharide, which showed strong temporal variations in suspended matter. In contrast, the wt % concentrations of individual monosaccharides showed large temporal differences for the fouling products, which were strongly influenced by the period of immersion and the type of test substratum. Glucose and fucose were relatively more abundant in the fouling products on SS and Cu, whilst glucose was the most abundant monosaccharide on MS. The monosaccharide and chemical composition data suggest strong temporal changes in the composition of the fouling products.     

Abundance of macroalgal organic matter in biofilms: evidence from n-alkane biomarkers

Biofilm development on titanium panels immersed in the surface waters of Dona Paula Bay was investigated using molecular biomarkers such as n-alkanes and other chemical and biological parameters. Biofilm biomass measured as organic carbon (OC), organic nitrogen (ON), chlorophyll a, diatoms and bacterial numbers on the titanium panels generally increased over the period of immersion. Total lipids and n-alkane concentration also showed similar trends. n-alkanes from C(12) to C(30) were detected in the biofilm samples, which showed a bimodal distribution. The first mode consisted of n-alkanes > C(23) with a strong even over odd predominance. In the second mode, the n-alkanes < C(23) were more abundant with odd carbon number maxima at C(15), C(17) and C(19) and a strong odd over even carbon number predominance (Carbon Preference Index > 2). The predominance of these odd-chain n-alkanes strongly indicates that the organic matter derived from macroalgal sources was the major contributor to the biofilm organic matter developed on the titanium panels over the 15 d period of study. The data suggest that molecular characterization is a useful tool in understanding the sources of biofilm organic matter. The observed abundance of macroalgal organic matter during the 15 d period of biofilm development may play an important role in subsequent fouling by micro- and macrofouling organisms.     

Biosynthesis of amino acids in Clostridium pasteurianum

1. Clostridium pasteurianum was grown on a synthetic medium with the following carbon sources: (a) (14)C-labelled glucose, alone or with unlabelled aspartate or glutamate, or (b) unlabelled glucose plus (14)C-labelled aspartate, glutamate, threonine, serine or glycine. The incorporation of (14)C into the amino acids of the cell protein was examined. 2. In both series of experiments carbon from exogenous glutamate was incorporated into proline and arginine; carbon from aspartate was incorporated into glutamate, proline, arginine, lysine, methionine, threonine, isoleucine, glycine and serine. Incorporations from the other exogenous amino acids indicated the metabolic sequence: aspartate --> threonine --> glycine right harpoon over left harpoon serine. 3. The following activities were demonstrated in cell-free extracts of the organism: (a) the formation of aspartate by carboxylation of phosphoenolpyruvate or pyruvate, followed by transamination; (b) the individual reactions of the tricarboxylic acid route to 2-oxoglutarate from oxaloacetate; glutamate dehydrogenase was not detected; (c) the conversion of aspartate into threonine via homoserine; (d) the conversion of threonine into glycine by a constitutive threonine aldolase; (e) serine transaminase, phosphoserine transaminase, glycerate dehydrogenase and phosphoglycerate dehydrogenase. This last activity was abnormally high. 4. The combined evidence indicates that in C. pasteurianum the biosynthetic role of aspartate and glutamate is generally similar to that in aerobic and facultatively aerobic organisms, but that glycine is synthesized from glucose via aspartate and threonine.     

Utilization of l-threonine by a species of Arthrobacter. A novel catabolic role for `aminoacetone synthase''

1. A species of Arthrobacter (designated Arthrobacter 9759) was isolated from soil by its ability to grow aerobically on l-threonine as sole source of carbon atoms, nitrogen atoms and energy; the organism also grew well on other sources of carbon atoms including glycine, but no growth was obtainable on aminoacetone or dl-1-aminopropan-2-ol. 2. During growth on threonine, (14)C from l-[U-(14)C]threonine was rapidly incorporated into glycine and citrate, and thereafter into serine, alanine, aspartate and glutamate. 3. With extracts of threonine-grown cells supplied with l-[U-(14)C]threonine, evidence was obtained of the NAD and CoA-dependent catabolism of l-threonine to produce acetyl-CoA plus glycine. Short-term incorporation studies in which [2-(14)C]acetate and [2-(14)C]glycine were supplied (a) to cultures growing on threonine, and (b) to extracts of threonine-grown cells, showed that the acetyl-CoA was metabolized via the tricarboxylic acid cycle and glyoxylate cycle whereas the glycine was converted into pyruvate via the folate-dependent ;serine pathway'. 4. The threonine-grown organism contained ;biosynthetic' threonine dehydratase and a potent NAD-linked l-threonine dehydrogenase but possessed no l-threonine aldolase activity. 5. Evidence was obtained that the acetyl-CoA and glycine produced from l-threonine had their immediate origin in the alpha-amino-beta-oxobutyrate formed by the threonine dehydrogenase; the CoA-dependent cleavage of this compound was catalysed by an alpha-amino-beta-oxobutyrate CoA-ligase, which was identified with ;aminoacetone synthase'. A continuous spectrophotometric assay of this enzyme was developed, and it was found to be inducibly synthesized only during growth on threonine and not during growth on acetate plus glycine. 6. By using a reconstituted mixture of separately purified l-threonine dehydrogenase and alpha-amino-beta-oxobutyrate CoA-ligase (i.e. ;aminoacetone synthase'), l-[U-(14)C]threonine was broken down to [(14)C]glycine plus [(14)C]acetyl-CoA (trapped as [(14)C]citrate). 7. There was no evidence of aminoacetone metabolism by Arthrobacter 9759 even though a small amount of this amino ketone appeared in the culture medium during growth on threonine.     

Hydroxy amino acid metabolism in Pseudomonas cepacia: role of L-serine deaminase in dissimilation of serine, glycine, and threonine.

Growth of Pseudomonas cepacia (P. multivorans) on serine depended upon induction of a previously undescribed L-serine deaminase distinct from threonine deaminase. Formation of the enzyme was induced during growth on serine, glycine, or threonine. The induction pattern reflected a role of the enzyme in catabolism of these three amino acids. Both threonine and glycine supported growth of serine auxotrophs and were presumably converted to serine and pyruvate in the course of their degradation. Mutant strains deficient in serine deaminase, or unable to use pyruvate as a carbon source, failed to utilize serine or glycine and grew poorly with threonine, whereas strains deficient in threonine dehydrogenase or alpha-amino beta-ketobutyrate:coenzyme A ligase (which together convert threonine to glycine and acetyl coenzyme A) failed to utilize threonine or derepress serine deaminase in the presence of this amino acid. The results confirm for the first time the role of alpha-amin beta-ketobutyrate:coenzyme A ligase in threonine degradation and indicate that threonine does not mimic serine as an inducer of serine deaminase.     

Abundance of Macroalgal Organic Matter in Biofilms: Evidence from n-Alkane Biomarkers

Biofilm development on titanium panels immersed in the surface waters of Dona Paula Bay was investigated using molecular biomarkers such as n-alkanes and other chemical and biological parameters. Biofilm biomass measured as organic carbon (OC), organic nitrogen (ON), chlorophyll a, diatoms and bacterial numbers on the titanium panels generally increased over the period of immersion. Total lipids and n-alkane concentration also showed similar trends. n-alkanes from C₁₂ to C₃₀ were detected in the biofilm samples, which showed a bimodal distribution. The first mode consisted of n-alkanes > C₂₃ with a strong even over odd predominance. In the second mode, the n-alkanes < C₂₃ were more abundant with odd carbon number maxima at C₁₅, C₁₇ and C₁₉ and a strong odd over even carbon number predominance (Carbon Preference Index > 2). The predominance of these odd-chain n-alkanes strongly indicates that the organic matter derived from macroalgal sources was the major contributor to the biofilm organic matter developed on the titanium panels over the 15 d period of study. The data suggest that molecular characterization is a useful tool in understanding the sources of biofilm organic matter. The observed abundance of macroalgal organic matter during the 15 d period of biofilm development may play an important role in subsequent fouling by micro- and macrofouling organisms.     

Different types of nitrogen deposition show variable effects on the soil carbon cycle process of temperate forests

Nitrogen (N) deposition significantly affects the soil carbon (C) cycle process of forests. However, the influence of different types of N on it still remained unclear. In this work, ammonium nitrate was selected as an inorganic N (IN) source, while urea and glycine were chosen as organic N (ON) sources. Different ratios of IN to ON (1 : 4, 2 : 3, 3 : 2, 4 : 1, and 5 : 0) were mixed with equal total amounts and then used to fertilize temperate forest soils for 2 years. Results showed that IN deposition inhibited soil C cycle processes, such as soil respiration, soil organic C decomposition, and enzymatic activities, and induced the accumulation of recalcitrant organic C. By contrast, ON deposition promoted these processes. Addition of ON also resulted in accelerated transformation of recalcitrant compounds into labile compounds and increased CO₂ efflux. Meanwhile, greater ON deposition may convert C sequestration in forest soils into C source. These results indicated the importance of the IN to ON ratio in controlling the soil C cycle, which can consequently change the ecological effect of N deposition.     

Glycine origin of the methyl substituent on C7'-N of octodiose for the biosynthesis of apramycin

Apramycin is unique in the aminoglycoside family due to its octodiose moiety. However, either the biosynthesis process or the precursors involved are largely unknown. Addition of glycine, as well as serine or threonine, to the Streptomyces tenebrabrius UD2 fermentation medium substantially increases the production of apramycin with little effect on the growth of mycelia, indicating that glycine and/or serine might be involved in the biosynthesis of apramycin. The 13C-NMR analysis of [2-13C] glycine-fed (25% enrichment) apramycin showed that glycine specifically and efficiently incorporated into the only N-CH3 substituent of apramycin on the C7' of the octodiose moiety. We noticed that the in vivo concentration of S-adenosyl methionine increased in parallel with the addition of glycine, while the addition of methione in the fermentation medium significantly decreased the productivity of apramycin. Therefore, the methyl donor function of glycine is proposed to be involved in the methionine cycle but methionine itself was proposed to inhibit the methylation and methyl transfer processes as previously reported for the case of rapamycin. The 15N NMR spectra of [2-13C,15N]serine labeled apramycin indicated that serine may also act as a limiting precursor contributing to the -NH2 substituents of apramycin.     

Hemolymph patterns of free amino acids in the brine shrimp Artemia franciscana after three days starvation at different salinities

The hemolymph pattern of free amino acids was examined in the brine shrimp, Artemia franciscana (Great Salt Lake origin). After one-month acclimation to 35 or 60 ppt salinity at 27 degrees C, the animals were transferred to 10, 35 or 60 ppt salinities to continue acclimation for 3 days without feeding at 27 degrees C. The osmolarity of one of the new media was raised by glycerol addition. In the hemolymph, 8 amino acids such as taurine, alanine, threonine, serine, lysine, glycine, arginine and leucine, comprised approximately 70% of the total content of free amino acids. This pattern suggested internal proteolysis due to starvation at high temperature. The total content of free amino acids significantly increased at 10 and 60 ppt salinities in comparison to 35 ppt. The hemolymph patterns from the 10 ppt and glycerol-added media showed a singularly high peak of taurine or alanine.     

Utility of amino acids as biomarkers in polar marine sediments: a study on the continental shelf of Larsen region, Eastern Antarctic Peninsula

Ongoing global warming is affecting the polar regions at a faster pace than in many other lower latitude environments. Based on the idea that the changes at the sea surface leave a signal in the sedimentary record, we analysed the total hydrolysable amino acid (THAA) and enzymatically hydrolysable amino acid (EHAA) contents in sediments off the coast of the eastern Antarctic Peninsula during the decade following the collapse of sections A and B of the Larsen ice shelf to check their utility as biomarkers of this event. Two organic matter lability indexes (the EHAA-to-THAA ratio and the Dauwe degradation index) were also calculated to assess the quality of the organic matter in the sediment column. The THAA and EHAA concentrations in the upper 5 mm varied between ~1 and ~10 nmol mg^?1 DW^?1, corresponding to an oligotrophic environment, whereas the quality of the organic matter as indicated by the lability indexes was relatively high in the upper sediment column (<2 cm deep). The amino acid profiles and indexes in the sediment column were compared to the pigment profiles and indexes published in previous studies for the same stations. The results suggest that in the sediment column, pigments track more accurately than amino acids the pelagic organic matter supply to the seabed after the collapse of the Larsen ice shelf.     

Fluorescence and amino acid characteristics of molecular size fractions of DOM in the waters of Lake Biwa

Dissolved organic matter (DOM) in the waters from Lake Biwa, Japan was fractionated using tangential flow ultrafiltration, and subsequently characterized by fluorescence properties and amino acids. While major dissolved organic carbon (DOC), UV absorbance (Abs), humic-like fluorescence (Flu) and total hydrolyzed amino acids (THAA) occurred in the less than 5 kDa molecular size fraction, they were not evenly distributed among various molecular size fractions. Flu/Abs ratios increased, and THAA/DOC ratios decreased with decreasing molecular size. Humic-like fluorescence occurred in all molecular size fractions, but protein-like fluorescence only occurred in the 0.1 m-GF/F fraction. Subtle differences in amino acid compositions (both individuals and functional groups) were observed between various molecular size fractions, this may indicate the occurrence of DOM degradation from higher to lower molecular weight. The results reported here have significance for further understanding the sources and nature of DOM in aquatic environments.     

Threonine formation via the coupled activity of 2-amino-3-ketobutyrate coenzyme A lyase and threonine dehydrogenase.

The enzymes L-threonine dehydrogenase and 2-amino-3-ketobutyrate coenzyme A (CoA) lyase are known to catalyze the net conversion of L-threonine plus NAD+ plus CoA to NADH plus glycine plus acetyl-CoA. When homogeneous preparations of these two enzymes from Escherichia coli were incubated together for 40 min at 25 degrees C with glycine, acetyl-CoA, and NADH, a 36% decrease in the level of glycine (with concomitant NADH oxidation) was matched by formation of an equivalent amount of threonine, indicating that this coupled sequence of enzyme-catalyzed reactions is reversible in vitro. Several experimental factors that affect the efficiency of this conversion in vitro were examined. A constructed strain of E. coli, MD901 (glyA thrB/C tdh), was unable to grow unless both glycine and threonine were added to defined rich medium. Introduction of the plasmid pDR121 (tdh+kbl+) into this strain enabled the cells to grow in the presence of either added glycine or threonine, indicating that interconversion of these two amino acids occurred. Threonine that was isolated from the total pool of cellular protein of MD901/pDR121 had the same specific radioactivity as the [14C]glycine added to the medium, establishing that threonine was formed exclusively from glycine in this strain. Comparative growth rate studies with several strains of E. coli containing plasmid pDR121, together with the finding that kcat values of pure E. coli 2-amino-3-ketobutyrate CoA lyase favor the cleavage of 2-amino-3-ketobutyrate over its formation by a factor of 50, indicate that the biosynthesis of threonine is less efficient than glycine formation via the coupled threonine dehydrogenase-2-amino-3-ketobutyrate lyase reactions.     

A general method for determining the contribution of split pathways in metabolite production in the yeast Saccharomyces cerevisiae

We describe a simple method using (13)C labeling and NMR spectroscopy to determine the flux contributions of alternative pathways in Saccharomyces cerevisiae that produce the same metabolite with identical labeling patterns. Cells were incubated with a (13)C-labeled precursor for one of the branches, and the absolute enrichment of the product and its metabolic precursor(s) was quantified. The ratio of the absolute enrichment of the product to that of its precursor reflects the contribution of the pathway. The method was applied to the biosynthesis of glycine in yeast, which can occur from threonine via threonine aldolase or from serine via serine hydroxymethyltransferase. [2-(13)C]Aspartate and [2-(13)C]serine were used as labeled precursors for the threonine aldolase and serine hydroxymethyltransferase pathways, respectively. The data show that in cells possessing both pathways, the serine hydroxymethyltransferase pathway contributes 65-75% of the total glycine production. In comparison with other approaches, this method provides an inexpensive, flexible alternative to determining the flux contributions of split pathways under controlled conditions and should have wide applicability in the metabolic engineering of microorganisms.     

Concentrations of free glucogenic amino acids in livers of rats subjected to various metabolic stresses

1. The concentrations of alanine, aspartate, glutamate, glutamine and serine plus threonine have been measured by enzymic methods in ;quick-frozen' livers from normal, starved, alloxan-diabetic and phlorrhizin-treated rats. 2. The hepatic concentrations of alanine and serine plus threonine were decreased in rats starved for 48hr. Treatment of these rats with phlorrhizin resulted in a rapid fall (within 2(1/2)hr.) in the concentrations of all the glucogenic amino acids except serine plus threonine, which increased. The pattern for alloxan-diabetic rats was similar to that for phlorrhizin-treated animals, except that here serine plus threonine also decreased in concentration. 3. The effects of anoxia on the hepatic concentrations of the glucogenic amino acids are reported. 4. Inhibition of glutamate-pyruvate transaminase in vivo by l-cycloserine resulted in the accumulation of alanine in situations involving high rates of gluconeogenesis from endogenous amino acids. 5. Measurements of the concentrations of the reactants of the glutamate-pyruvate transaminase and glutamate-oxoglutarate transaminase systems in various metabolic states suggest that they are both at or near equilibrium in rat liver. 6. New enzymic methods are described for the determination of serine plus threonine and alanine.     

Amino acid composition of rat and human liver microsomes in normal and pathological conditions

The amino acid composition of proteins from liver microsomes has been studied in rats and in human subjects with normal liver, with obstructive jaundice or liver cirrhosis. The pattern of the amino acid composition of microsomes appeared to be species-specific. Phenylalanine, threonine, serine, proline, histidine and [aspartic acid plus asparagine] were increased, while alanine, tyrosine, glycine and arginine were decreased in the human compared to the rat microsomes. In patients with obstructive jaundice of short duration (less than two months) only a slight decrease in leucine and phenylalanine could be noticed, while in the case of liver cirrhosis amino acid composition was markedly changed.     

Observation on Plasma Free Amino Acids of Cow under Different Feeding

The influence of nutritional alteration to the plasma amino acid patterns in cows was investigated. The ratio of the essential to nonessential amino acids (E/N) at 6 months after change of diet was higher in the group fed a high protein and low energy diet than the group fed a moderate protein and moderate energy diet (the control group). The total nonessential amino acid levels decreased in the former group. The decrease was due to lower values for glycine, alanine and glutamic acid.

On the other hand, the E/N radio was lower in groups fed low protein diets than in the control group and total essential amino acid levels were lower in the former group than in the control group. The decrease was due to lower values for valine, threonine and arginine. Conversely, the higher values in glycine, serine and proline than those in the control group were observed.     

Chemical characterization of a marine conditioning film

Conditioning film grown on glass panels was analyzed for organic carbon and nitrogen, total carbohydrates, aldoses, uronic acids, and proteins. These compounds showed non-linear increase over the period of immersion. Total carbohydrate-C, aldose-C, uronic acid-C, and protein-C accounted for 5.59–23.50%, 0.6–5%, 1–5%, and 4–14% of organic carbon, respectively, while aldose-C accounted for 10–72% of the total carbohydrate-C. Aldoses such as rhamnose, arabinose, xylose, mannose, and glucose were generally present in the conditioning film. A principal component analysis based on weight percentages of aldoses established three factors that contributed ～77% of the total variance. The first factor was influenced by the abundance of rhamnose and accounted for 41% of the total variance. The second factor was influenced by the concentrations of arabinose and xylose, whereas the third factor was controlled by ribose and galactose, thereby implicating the role of terrestrial and microbial input to the conditioning film. These changes in the chemistry of the conditioning film may play some role in influencing microbial adhesion to surfaces.     

Gluconeogenesis from glycine and serine in fasted normal and diabetic rats.

1. Non-anaesthetized normal and diabetic rats were fasted for 1 day, and [U-14C]glycine, or [U-14C]serine, or [U-14C]- plus [3-3H]-glucose was injected intra-arterially. The rates of synthesis de novo/irreversible disposal for glycine, serine and glucose, as well as the contribution of carbon atoms by the amino acids to plasma glucose, were calculated from the integrals of the specific-radioactivity-versus-time curves in plasma. 2. The concentrations of both glycine and serine in blood plasma were lower in diabetic than in fasted normal animals. 3. The rates of synthesis de novo/irreversible disposal of both amino acids tended to be lower in diabetic animals, but the decrease was statistically significant only for serine (14.3 compared with 10.5 mumol/min per kg). 4. Of the carbon atoms of plasma glucose, 2.9% arose from glycine in both fasted normal and diabetic rats, whereas 4.46% of glucose carbon originated from serine in fasted normal and 6.77% in diabetic rats. 5. As judged by their specific radioactivities, plasma serine and glycine exchange carbon atoms rapidly and extensively. 6. It was concluded that the turnover of glycine remains essentially unchanged, whereas that of serine is decreased in diabetic as compared with fasted normal rats. The plasma concentration of both amino acids was lower in diabetic rats. Both glycine and serine are glucogenic. In diabetic rats the contribution of carbon atoms from glycine to glucose increases in direct proportion to the increased glucose turnover, whereas the contribution by serine becomes also proportionally higher.