Inosine monophosphate, oxidation

Figure 34-2 illustrates the intermediates and reactions for conversion of a-D-ribose 5-phosphate to inosine monophosphate (IMP). Separate branches then lead to AMP and GMP (Figure 34-3). Subsequent phosphoryl transfer from ATP converts AMP and GMP to ADP and GDP. Conversion of GDP to GTP involves a second phosphoryl transfer from ATP, whereas conversion of ADP to ATP is achieved primarily by oxidative phosphorylation (see Chapter 12).

Although the major route for aspartate degradation involves its conversion to oxaloacetate, carbons from aspartate can form fumarate in the urea cycle (see Chapter 38). This reaction generates cytosolic fumarate, which must be converted to malate (using cytoplasmic fumarase) for transport into the mitochondria for oxidative or anaplerotic purposes. An analogous sequence of reactions occurs in the purine nucleotide cycle. Aspartate reacts with inosine monophosphate (IMP) to... 

Nitrosyl chloride added portionwise to an ice-salt-cooled suspension of adenosine N -oxide 5 -monophosphate in dimethylformamide, and allowed to warm to room temp, during ca. 1.5 hrs. inosine N -oxide 5 -monophosphate. Y 90.5% as the mono-Na-salt. F. e. s. H. Sigel and H. Brintzinger, Helv. 48, 433 (1965). 

However, as shown in Scheme 14.3, some of which has been seen earlier as Scheme 12.111 in Section H of Chapter 12) inosine phosphate, also can undergo hydration at C2. Oxidation of the resulting carbinolamine in the presence of inosine monophosphate dehydrogenase (EC 1.1.1.205) produces xanthosine 5 -phosphate. The xanthosine 5 -phosphate is then converted to guanosine 5 -monophosphate (GMP). 

The conversion of the adenine ring to guanine takes place by the deamination of AMP to inosine monophosphate (IMP), followed by oxidation of IMP to xanthosine monophosphate (XMP) and amination of XMP to GMP. Bacterial mutants which lack either the dehydrogenase or the aminase cannot convert adenine to nucleic acid guanine (19,20). In general the interconversion of purines does not take place by reversible reactions operating in either direction. 

Modification of inosine 5 -monophosphate occurs by two routes oxidation by an NAD requiring enzyme to the 2-oxopurine and hence to guanosine 5 -monophosphate, or aspartate dependent amination at C-6 by a sequence similar to that employed in the conversion of (16) to (18) described above to give adenine 5 -monophosphate. 

Immobilized metal-affinity chromatography Na+-dependent alanine-insensitive proline uptake system (SLC6A20) Integrin-mobilferrin pathway membrane protein system involved in the transport of ferric iron also inosine-5 - monophosphate Inducible oxide synthetase Iifitiator element Inositol 1,4,5-triphosphate Immobilized pH gradient Isopropylthio-p-D-galactosidase Isopropylthio-p-D-galactopyranoside Inverted repeat insulin receptor... 

Lipid oxidation products and their reaction products with amino acids (proteins) have a considerable influence on the typical odour and taste of meat. Particularly significant aminocarboxylic acids include glutamic acid, alanine, threonine and lysine, guanidine compounds (creatine and creatinine), quaternary ammonium compounds (choline and carnitine), peptides (P-alanylhistidine peptides and some products of proteolysis), free nucleotides, nucleosides and their bases (especially inosine 5 -monophosphate, IMP), proteins, carboxylic acids (especially lactic acid), sugars (mainly glucose, fructose and their phosphates, ribose formed by hydrolysis of free nucleotides) and some vitamins (especially thiamine). Some of these compounds, such as glutamic acid and IMP, are additionally used as food additives, namely as flavour enhancers. 

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