Glycine labeled with

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. 

Urate metabolism was defined by a technique which has been evolved by many investigators over the years. This involved the determination of urate pool and turnover by isotope dilution following the intravenous injection of labelled urate, with the simultaneous measurement of the percent incorporation of glycine labelled with an alternative isotopic label ( C) and determination of its percent incorporation into urinary, and also into produced urate, within a 7 day period. (Methods detailed in "The Effect of Weight Reduction on Urate Metabolism"). 

This enzyme catalyzes the conversion of pyruvate to formate and acetyl CoA and is a key enzyme in the anaerobic degradation of carbohydrates in some Enterobacteriaceae. Using an enzyme selectively C-labeled with glycine, it was shown by EPR that the reaction involves production of a free radical at C-2 of glycine (Wagner et al. 1992). This was confirmed by destruction of the radical with O2, and determination of part of the structure of the small protein that contained an oxalyl residue originating from gly-734. 

Fig. 5. Subdivisions of the phi/psi or Ramachandran map labeled with the range of propensities for the 18 amino acids (glycine and proline are excluded) as they map to each subdivision calculated from a large collection of folded protein structures. The propensity is defined by the probability that amino acid x will be found in a subdivision divided by the probability that an average amino acid will be found in a subregion. Data are taken from Table 1 of Shortle (2002).

Figure 2-18 Typical (3 bulges in antiparallel pleated sheets. The residues Rx, R2, and Rx identify the bulges. (A) A "classic" (3 bulge, in which < )[ and /j are nearly those of an a helix while other torsion angles are approximately those of regular (3 structures. (B) The G1 bulge in which the first residue is glycine with = 85°, /j = 0°. It is attached to a type II (3 turn of which the glycine (labeled 1) is the third residue.

The thermal decarboxylation of NCA s involves the 2-carbonyl group of the oxazolidine-2,5-dione ring. This was proved (9) by labelling glycine NCA with C13 and examining the C13 content of the carbon dioxide evolved in thermal polymerisation. 

A more extensive study of mobilities of 3H- and 14C-labeled amino acids again found that amino acids labeled with 14C at Cl or C2 are retained on the column, relative to the unlabeled forms.135 Lysine is an exception. Tritiation at C3 also increases the retention time, but tritiation at C2 of glycine or at C4, C5, or C6 of lysine decreases it, and large decreases are seen with methionine tritium-labeled in the methyl and with tyrosine tritium-labeled at C3, 5. The 14C IEs can be attributed to a decrease of acidity, but the IEs of distant 3H may be due to hydrophobic interactions with the resin. A remarkable result is that intramolecular isotopic isomers (isotopomers) can be distinguished on the basis of their chromatographic mobilities. 

The glucose-glycine reaction has therefore been reinvestigated using glucose labelled with 90 % at C-1. The behavior of a few potential intermediates under similar reaction conditions has also been studied. 

Insulin was reacted with Sanger s reagent and then completely hydrolyzed. Two amino acids, a glycine and a phenylalanine, were found to be labeled with the 2,4-dinitrophenyl group. 

This experiment indicates that there must be two N-terminal amino acids because two amino acids were labeled with the DNP group. Therefore, there must be two polypeptide chains, connected by disulfide linkages. One has glycine as its N-terminus and the other has phenylalanine. 

Fig. 33. Outline of the biosynthesis of uroporphyrinogen III (abbreviated urogen III), Starting with glycine labelled at position 2. The label is distributed as indicated with filled circles. The carboxyl group of glycine is lost as carbon dioxide. A = acetic acid side chain P = propionic acid side chain.

Aminolevulinic acid (ALA), labelled with 13C at C(1). C(2), C(3), C(4) and C(5), has been synthesized64 from 13C-labelled KCN, glycine, Meldrum s acid or bromoacetate, prepared in turn from 13C-sodium acetate or 13C-acetic acid (equations 26 and 27). It was used for direct observation of the enzymatic transformation of ALA to porphobilinogen (PBG) by 13C-high-field FT-NMR spectroscopy without chemical degradation of the intermediate and the compounds. 

Fig. 2.18 Graph set assignments for the binary level of a-glycine. As in Fig. 2.17, different types of hydrogen bonds (solid lines) are distinguished by labelling with lower case bold letters carbon and hydrogen atoms are shown as open circles, oxygen atoms as solid circles, and nitrogen atoms as shaded circles. (From Bernstein and Davis 1999, with permission.)...

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