[Show abstract][Hide abstract] ABSTRACT: In a previous paper (Dickens & Glock, 1951) it was shown that at least two liver factors are necessary for the oxidation of D-ribose-5-phosphate, one being a coenzyme ii-(triphosphopyridine nucleotide; TPN)-specific dehydrogenase and the other an aldolase. Two alternative mechanisms of oxidation were suggested. The first involves an aldolase split into triosephosphate and a C2 fragment, synthesis of hexosemonophosphate from two C. molecules and subsequent oxidation through the appropriate TPN-specific system. The second alternative is the direct oxidation of D-ribose-5-phosphate to 5-phospho-D-ribonic acid followed by oxidative decarboxylation as suggested by Dickens (1936, 1938) for yeast. It has now been shown that this direct oxidative pathway is unlikely to occur, at least in liver. Synthesis of hexosemonophosphate, already demonstrated by Dische (1938, 1949) with haemolysed human erythrocytes and by Schlenk & Waldvogel (1947) and Waldvogel & Schlenk (1947, 1949) with rabbit-liver preparations, has been found to occur very rapidly and to such an extent as to exclude its formation solely from triosephosphate derived from breakdown of pentosephosphate.
[Show abstract][Hide abstract] ABSTRACT: In the context of a "glyoxylate scenario" of primordial metabolism, the reactions of dihydroxyfumarate (DHF) with reactive small molecule aldehydes (e.g., glyoxylate, formaldehyde, glycolaldehyde, and glyceraldehyde) in water were investigated and shown to form dihydroxyacetone, tetrulose, and the two pentuloses, with almost quantitative conversion. The practically clean and selective formation of ketoses in these reactions, with no detectable admixture of aldoses, stands in stark contrast to the formose reaction, where a complex mixture of linear and branched aldoses and ketoses are produced. These results suggest that the reaction of DHF with aldehydes could constitute a reasonable pathway for the formation of carbohydrates and allow for alternative potential prebiotic scenarios to the formose reaction to be considered.
Journal of the American Chemical Society 02/2012; 134(7):3577-89. · 10.68 Impact Factor
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