Methylglyoxal triose

Gugliucci, A., Smith, M. E., and Menini, T. (2002). Carnosine in physiological concentrations inhibits advanced glycation of histones by reactive trioses methylglyoxal and glyceralde-... 

Although enzymes tend to be extremely specific they are not always completely able to avoid side reactions. Triose phosphate isomerase releases small amounts of methylglyoxal (Eq. 13-28), presumably as... 

The rather toxic methylglyoxal is formed in many organisms and within human tissues.174 It arises in part as a side reaction of triose phosphate isomerase (Eq. 13-28) and also from oxidation of acetone (Eq. 17-7) or aminoacetone, a metabolite of threonine (Chapter 24).175 In addition, yeast and some bacteria, including E. coli, have a methylglyoxal synthase that converts dihydroxyacetone to methylglyoxal, apparently using a mechanism similar to that of triose phosphate isomerase. It presumably forms enediolate 2 of Eq. 13-26, which eliminates inorganic phosphate to yield methyl-... 

The enediolate is stabilised to phosphate loss by the protein of triose phosphate isomerase, but occasionally comes off the enzyme and yields methylglyoxal, which is detoxified by another hydroxy ketone isomerase, glyoxylase. 

The role of enediols in the conversion of L-glyceraldehyde 3-phosphate (26) into either dihydroxyacetone phosphate (27) or inorganic phosphate plus methylglyoxal (28) has been postulated for some time. Triose phosphate isomerase, which does not react with (26) directly, can convert it into dihydroxyacetone phosphate by... 

Phillips SA, Thornalley PJ (1993) The formation of methylglyoxal from triose phosphates. Eur J Biochem 212 101-105... 

In the reaction mixtures of the action of alkali on hexoses, small amounts of methylglyoxal (pyruvic aldehyde) and much lactic acid appear this is proof that the molecule is sensitive to a cleavage of some kind at the center of the chain. These products also occur in the alkali-treated solutions of trioses, along with traces of acetol, lactic aldehyde, and pyruvic acid 74, 93). However, the trioses so rapidly condense to sugars that the appearance of common reaction products does not establish the sequence of reactions. If trioses deliberately are added to an alkaline hexose solution... 

The reaction of trioses takes place in a similar manner (Figure 4.50). D-Glyceraldehyde or 1,3-dihydroxyacetone dehydration yields 1,2-diulose methylglyoxal (also known as pyruvic acid aldehyde or pyruvaldehyde) and the intramolecular Cannizzaro reaction of methylglyoxal yields lactic acid (racemate). 

Figure 4.50 Formation of methylglyoxal and lactic acid from trioses.

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