Nitrogen, free amino

The major constituents of biomass are present at low levels in DOM. The median freshwater contains 1.3p,molL of total hydrolyzable amino acids, the most abundant of which are glycine (20%), aspartic acid (12%), alanine (10%), glutamic acid (9%), and serine (9%). Collectively, the amino acids account for 1.8% of the organic carbon in DOM and —18% of its nitrogen. Free amino acids also exist in freshwaters, but the median concentration of 0.3 p,mol is a factor of 4-5 lower than the concentration of bound amino acids. Elevated levels of serine and ornithine in the data set for free amino acids strongly suggest that some samples may have been contaminated by human fingerprints. 

Lassaigne s test is obviously a test also for carbon in the presence of nitrogen. It can be used therefore to detect nitrogen in carbon-free inorganic compounds, e.g., complex nitrites, amino-sulphonic acid derivatives, etc., but such compounds must before fusion with sodium be mixed with some non-volatile nitrogen-free organic compound such as starch... 

Another important method of following protein hydrolysis is that due to Van Slyke, and consists in estimating the free amino groups liberated by treatment with nitrous acid, whereby gaseous nitrogen is evolved and measured in a special apparatus. 

If the yeast does not get enough free amino nitrogen, the fermentation will be poor and the beer quaHty inferior. A neutral bacterial protease added at mashing-in can be used to raise the level of free amino nitrogen. This is useful when working with poorly modified malt or with high adjunct ratios. 

The nitrogen content in honey is about 0.04%. Amino acid content accounts for approximately 1% (w/w). Free amino acid profiles have been proposed for the determination of the botanical and geographical... 

Normally the reaction Is useful for the conversion of alkyl halides to primary amines without concomitant formation of secondary amines.29 Treatment of polymer 17 with hexamethylenetetramine in a mixture of ethanol/THF afforded an insoluble resin. Using diazabicyclooctane (DABCO), we demonstrated that the reaction could be limited to attack by a single nitrogen in a multifunctional amine, so we did not anticipate crosslinking via bis-quat salt formation. Hydrolysis of 2 with anhydrous HC1 in ethanol generated free amino groups as evidenced by a positive ninhydrin test, but quantitative hydrolysis could not be achieved and the product remained insoluble. One would have expected a simple bis-quat to hydrolyse and open the crosslinked structure. 

The use of nitrogen fertilization results in higher content of N-containing compounds, including free amino acids, and also increases in terpene content in wood plants, whilst starch, total carbohydrates, phenylpropanoids and total carbon-based phytochemicals decreased (Koricheva et al., 1998). Higher levels of nitrogen favoured its uptake and increased the nitrate content of the crop, which is critical for salad vegetables and baby foods. 

More data are needed on the effects of organic practices on phytochemicals and their precursors. How does modification of precursor pools affect biosynthesis For example, see studies on the effects of lower levels of free amino acids caused by a reduction in nitrogen input. 

The neomycin molecule contains both free amino and free hydroxy groups. Many workers have exploited the possibility of chemical de-rivatisation at these positions in attempts to reduce the toxicity of the parent antibiotic. Substitution of methane sulphonate groups at the amino nitrogen has been reported by Umezawa et al83,84 and by Boissier et al . Both groups of workers described the derivative to be less toxic... 

In addition to the asymmetric induction mentioned above, sultam 53 can also be used to prepare enantiomerically pure amino acids (Scheme 2-29 and Table 2-10).55 Me AI-mediated acylation of 53 with methyl A-[bis(methylthio)-methylene]glycinate 56 provided, after crystallization, glycinate 57, which can serve as a common precursor for various a-amino acids. In agreement with a kinetically controlled formation of chelated (Z)-enolates, alkylation happened from the SZ-face of the a-C, opposite to the lone pair electrons on the sultam nitrogen atom. High overall yield for both the free amino acid 58 and the... 

Although these experiments showed growth was possible using casein hydrolysate, Rose also demonstrated that when the amino acid mixture was used rather than the intact protein, additional calories had to be provided as fat plus carbohydrate, if nitrogen balance was to be maintained. It was later shown that the carbohydrate was needed to protect the free amino acids from oxidation in the intestinal epithelium in the course of absorption. Further, amino acids are poorly tolerated by mouth, causing vomiting and/or diarrhea. After World War II attempts to feed very emaciated prisoners in concentration camps with protein hydrolysates were unsuccessful. It was then recognized that osmotic effects from the amino acids were responsible for the unpleasant consequences. 

The Klotz group has also found rate enhancements of decarboxylation reactions with PEI derivatives. Catalysis of decarboxylation of j -keto acids by small amines goes via a Schiff base intermediate. Mine s group has shown that unmodified PEI catalyzes dedeuteration effectively and that the reactions involve Schiff base intermediates 34, and references therein). Dodecyl-PEI containing free amino groups and quaternized nitrogens, dodecyl-PEI-Q-NHj, was found to be an effective catalyst for the decomposition of oxaloacetate (reaction 12) (92). At pH 4.5 the polymer is 10 times as effective as ethylamine. was found to be 3.5 x 10 " M at pH 4.5. 

MacdowalP found that tobacco leaves were most susceptible to injury by ozone (at 0.035 ppm for 5 h) just after full leaf expansion. This point corresponded to the banning of the decline in protein content. Lee modified the nitn en content of tobacco leaves by supplying urea and found a positive correlation of injury caused by ozone (at 1 ppm for 5 h) with nonprotein nitrogen, but not with protein. This result is in contrast with that of Ting and Mukeiji, who found that, in cotton leaves (in which the period of maximal susceptibility was at about 75% of full leaf expansion), the amino acid pool was low at the time of maximal susceptibility. However, ozone treatment (0.7 ppm for 1 h) increased the free amino acid pool. 

There are at least two answers to question (i). First, abnormal proteins can arise in cells due to spontaneous denaturation, errors in protein synthesis, errors in post-translational processing, failure of the correct folding of the protein or damage by free radicals. They are then degraded and replaced by newly synthesised proteins. Secondly, turnover helps to maintain concentrations of free amino acids both within cells and in the blood. This is important to satisfy the requirements for synthesis of essential proteins and peptides (e.g. hormones) and some small nitrogen-containing compounds that play key roles in metabolism (see Table 8.4). 

The carbon in the isothiocyanate grouping is highly susceptible to nucleophilic attack by the peptide s free amino group. Overall addition to the C=N creates a thiourea derivative. Making the conditions strongly acidic then promotes nucleophilic attack by the sulfur of the thiourea on to the carbonyl of the first peptide bond, producing a five-membered thiazoline heterocycle. Proton loss occurs from the nitrogen, and this creates an intermediate that is equivalent to the addition product in simple acid-catalysed amide... 

Incorrect Each compound composes an amino sugar group and a nitrogen-free sugar group bound directly to a 14-membered-ring aglycon moiety. 

The relationship, if any, between the secondary metabolism of L-phenylalanine and carbohydrate degradation during brown-rot wood decay processes has not yet been determined. However, we suspect that the secondary metabolism of this aromatic amino-acid plays an important role in converting monomeric sugars to nitrogen-free metabolites (Shimada, M., and Takahashi, M., In Handbook of Wood and Cellulosic Materials Hon,... 

Figure 3.5 The synthesis of diazepam is initiated by the double acylation of an aromatic amine with an aromatic acid chloride. A second equivalent of the p-chloroaniline leads to a six-membered ring with two nitrogens. This is hydrolytically opened to expose a free amino group which reacts with an aminoester to yield a seven-member ring. The amide nitrogen is then methylated.

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