Glycines, isotopically labelled, synthesis

This year has seen the application of carbohydrates in the synthesis of enantiomerically pure acids, amino acids and diols, including those containing isotopic labels. l,2 5,6-Di- >-isopropylidene-a-D-glucofuranose has been converted to diastereomerically pure epoxide 102 and diol 103 and the reactivity of these units has been exploited for the synthesis of enantiomerically pure labelled glycine and acetic acid, as well as 1,2-diols (Scheme 2 )P ... 

Escherichia coli Adenine and adenosine are inhibitory74 and the synthesis of thiamine can be derepressed by culture in their presence.13,75 adth- Mutants are known.76 [l4C]Formate incorporates at C-2 of pyramine without dilution of molar activity. Glycine labeled with stable isotopes was fed to E. coli and the pyramine was analyzed by mass spectrometry. The two carbon atoms of glycine separated during the biosynthesis. The carboxyl was found12 at C-4, and the C-N fragment was the precursor of C-6-N-1. In conclusion, it is beyond doubt that pyramine synthesis follows the AIR pathway in E. coli. 

Changes in the rate of synthesis of nucleic acids as measured by the rate of incorporation of labeled precursors may be more informative than changes in nucleic acid concentrations in atrophying muscle. An enhanced incorporation of isotope into nucleic acids after glycine- C is administered to dystrophic mice (aged % to 2 months) was found by Coleman and Ashworth (Cl) the free glycine pool was the same in normal and dystrophic muscle. More extended studies have been reported by Srivastava (S14), who used uridine-2- C as a precursor of RNA. At 30 days of age the incorporation in the dystrophic muscle was higher than normal, but it was the same at 60 days and lower at 90 days. These differences were confirmed by in vitro incorporation experiments... 

Nyhan later described another patient who was a hyperexcretor and displayed the associated clinical symptoms. This child synthesized uric acid from labeled glycine 200 times as rapidly as did normal controls (N5). Another aspect of Nyhan s studies was the rapid decrease of labeled uric acid from patients given glycine- C. The fact that, a week after administration of the isotope, the radioactivity of uric acid in the control and the patients under study approached approximately the same value would seem to indicate that the initial large amount of labeled uric acid was formed by the synthesis of purine nucleotides, which were rapidly broken down and did not involve an increased turnover of nucleic acid per se. It reflects a labile nucleotide pool, not a highly labeled one. 

C-labelled glycines have been prepared " from the corresponding bromoacetic acids , used in the synthesis of the 2, 3, 5 -tri-C)-benzoyl[4- C]uridine and regiospecific introduction of isotopic carbon or nitrogen into one or more positions of the pyrimidine ring . [ N]glydne has been prepared from potassium [ N]phthalimide . 

In order to calculate the total amount of early labelled bilirubin produced after giving a labelled precursor of haem synthesis, both the isotope concentration of the bilirubin (in the case of this is the same as that of faecal sterco-bilin) and the total amount of bilirubin produced per day must be measured. The percentage incorporation of the precursor can then be calculated. When glycine is the precursor, comparison of the percentage incorporation into the ELP with the percentage incorporation into haem (equivalent to the late peak) allows the ELP to be expressed as a fraction of total bilirubin production, and hence in absolute values. 

Inasmuch as cytochrome c is a relatively small protein easily extractable and easily recognized by spectro-photometric methods, it is quite natural that its biosynthesis was investigated in vivo in a variety of tissues. Much of the in vivo work comes from Drabkin s laboratory [116]. These workers used labeled glycine as a precursor and followed its incorporation in both the heme and the protein moiety of cytochrome c. The following is a summary of their findings (1) the isotope is incorporated in both the porphyrin and the protein portion of the molecule (2) the incorporation is more rapid in the heme than in the protein fraction (3) practically all tissues are capable of independent cytochrome c synthesis (4) studies in regenerating liver also demonstrate that the rate of cytochrome c synthesis outweighs the active increase in the cellular population and (5) new cytochrome c is made in the endoplasmic reticulum and transferred by an unknown mechanism to mitochondria. 

Extracts of acetone-dried pigeon liver catalyze the synthesis of GSH from glutamic acid, cysteine, and glycine provided magnesium ions and ATP are added (2). Marked stimulation of sjmthesis is provided by potassium ions. After the removal of hydrolytic enzymes from the crude extract, a net synthesis of GSH can be demonstrated by means of the glyoxalase assay (2). The close correspondence between the values obtained by the glyoxalase assay and by the isotopic technique shows that in this system the incorporation of a labeled amino acid into GSH is a measure of de novo synthesis. 

The (9-carbon of serine as well as the a-carbon of glycine were extensively incorporated into the methyl group of thymine in the adult rat (334). In addition, formate-C served as a precursor of the methyl group of thymine both in vivo (29) and in vitro (335) formaldehyde was also utilized for thymine methyl group synthesis (336). Isotopic data indicated that the hydroxymethyl group of serine, doubly labeled with and D, was transferred to position 5 of thymine with a minimum of 1.5 atoms of D per carbon atom this demonstrated that the /3-carbon of serine was not metabolized all the way to formate (337),... 

An isotopic atom can be inserted into a molecule by chemical synthesis. Thus one can prepare e.g. glycine, which has in its a-position the -emitting carbon of atomic weight 14. The a-position of glycine is then said to be labeled with C. When one uses radioactive isotopes it suffices if only one out of ten thousand or a hundred thousand molecules contains the isotope. 

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