843505.fig.003a
(a)
843505.fig.003b
(b)
843505.fig.003c
(c)
843505.fig.003d
(d)
Figure 3: Formation of methylglyoxal and glyoxal in biological systems. (a) The acyclic form of glucose may undergo autooxidation via the Wolff pathway to form glyoxal or break down to 3-deoxyglucosone which in turn degrades to glyceraldehyde and methylglyoxal. Glucose may also react with amine groups on proteins to form a Schiff base which can undergo similar breakdown via the Namiki pathway to also generate glyoxal and methylglyoxal. (b) The major pathway by which methylglyoxal is formed in cells involves the breakdown of the triose phosphates, glyceraldehyde-3-phosphate, and dihydroxyacetone phosphate, via phosphate elimination from an ene-diol intermediate. (c) Methylglyoxal may also be generated during threonine catabolism. This involves oxidation of threonine by threonine dehydrogenase to 2-aminoacetoacetate, followed by spontaneous decarboxylation to aminoacetone. Monoamine oxidase then catalyses the conversion of aminoacetone to methylglyoxal. (d) Another pathway by which methylglyoxal is produced is from acetoacetate metabolism. This reaction proceeds via acetone and acetol and is catalysed by acetone monooxygenase and acetol monooxygenase.