Ribose reaction with tryptophan

The perchlorates of various secondary amines, such as diphenylamine and indole derivatives, are colorless.64 The similarity of colors produced in the presence of hydrochloric acid also attests to the non-auxochromic character of the perchlorate ion in the production of the colored derivative. Consequently, the only role attributable to the perchloric acid in this test is that with nucleic acids it leads to more effective hydrolysis and releases more 2-desoxyribose for reaction with tryptophan. This reaction leads to the production of a substance of the type represented by XV and XVI (R " = H), and the increase in the number of conjugated double bonds results in the product being colored. With ribose, which has a free hydroxyl group at carbon atom 2, a ketone of the type shown in XVII can be formed, and in this case the net result is no increase in the number of double bonds conjugated with the indole nucleus and no comparable increase in color. Hence the test will distinguish between ribose and 2-desoxyribose. 

It was mentioned above that the carboxyl carbon is lost in the conversion of anthranilic acid to indole. Consequently, two additional carbon atoms must be supplied to complete the pyrrole ring of the indole. The observation that various ribose derivatives could be the source of these two carbons provided the clue that led to the elucidation of the mechanism of indole synthesis in the tryptophan biosynthetic pathway (232). Yanofsky determined that sonic extracts of a tryptophan auxotroph of E. cdi (that also grew on anthranilic acid or indole) could utilize ribose, ribose 5-phosphate, and 5-phosphoribosylpyrophosphate to form indole from anthranilic acid. With the two former compounds, ATP was essential for the reaction, with the latter compound it was not. This result made it appear evident that 5-phosphoribosylpyrophosphate was the more immediate reactant in the condensation with anthranilic acid. 

The answer is a. (Murray, pp 627-661. Scriver, pp 3897-3964. Sack, pp 121—138. Wilson, pp 287-320.) The major contributor of electrons in reductive biosynthetic reactions is nicotinamide adenine dinucleotide phosphate (NADPH -I- H ), which is derived by reduction of NAD. NAD is formed from the vitamin niacin (also called nicotinate). Niacin can be formed from tryptophan in humans. In the synthesis of NAD, niacin reacts with 5-phosphoribosyl-l-pyrophosphate to form nicotinate ribonucleotide. Then, AMP is transferred from ATP to nicotinate ribonucleotide. Finally, the amide group of glutamate is transferred to the niacin carboxyl group to form the final product, NAD. NADP is derived from NAD by phosphorylation of the 2 -hydroxyl group of the adenine ribose moiety. The reduction of NADP to NADPH -I- H occurs primarily through the hexose monophosphate shunt. 

The pentose phosphate pathway is an alternative pathway for glucose degradation that is particularly abundant in the liver and adipose tissue. It provides the cell with a source of NADPH to serve as a reducing agent for bios)mthetic reactions. It also provides ribose-5-phosphate for nucleotide synthesis and erythrose-4-phosphate for bios)mthesis of the amino acids tryptophan, t)rrosine, and phenylalanine. 

For the biosynthesis of cell components a microorganism must be supplied with appropriate low molecular weight compounds such as sugars, organic acids, amino acids etc. Many of 2-, 3-, 4- and 5-carbon compounds are formed in catabolic reactions. In propionic acid bacteria these reactions comprise the propionic acid fermentation, TCA cycle and hexose monophosphate shunt. The latter supplies the cell with erythrose-phosphate, ribose-5-phosphate and reducing equivalents (NADPH) needed for many syntheses. Erythrose-4-phosphate is used in the formation of aromatic amino acids phenylalanine, tryptophane, tyrosine. Ribose-5-phosphate is incorporated into nucleic acids. The pentose cycle and propionic acid fermentation, as mentioned before, have a number of common precursors and enzymes. The inclusion of common precursors into one or another pathway is regulated by the level of ATP (Labory, 1970), and this regulation in fact determines the ratio of catabolic and anabolic processes in the cell. 

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