Dihydroxymandelic aldehyde

At adrenergic nerve terminals norepinephrine and epinephrine can be taken up, oxidized [via MAO] to 3,4-dihydroxymandelic aldehyde and thence oxidized to 3,4-dihydroxymandelic acid (DOMA) and 3,4-dihydroxyphenylglycol (DHPG). Extracellular DOMA and DHPG can then be converted via COMT to the methylated derivatives VMA and MHPG. 

As illustrated in Figure 4.10, noradrenaline (norepinephrine) may be )V-methylated in some human tissues. Deamination of either noradrenaline or adrenaline (epinephrine) leads to 3,4-dihydroxymandelic aldehyde, and this intermediate may be oxidised to 3,4-dihydroxymandelic acid (DHMA)... 

Figure 7.1 Pathways of synthesis and metabolism of catecholamines with enzymes catalyzing various reactions. (1) Tyrosine hydroxylase (2) aromatic amino acid decarboxylase (3) phenylamine-P-hydroxylase (4) phenylethanolamine-A-methyltransferase (5) monoamine oxidase plus aldehyde dehydrogenase (6) catechol-O-methyltransferase (7) conjugating enzymes about 95% phenolsulfo-transferase and 5% phenolglucuronatetransferase (in human). DOPA, dihydroxyphenylalanine DOMA, dihydroxymandelic acid DHPG, dihydroxyphenylglycol DOPAC, dihydroxyphenylacetic acid HVA, homovanillic acid MHPG, methoxyhydroxylphenylglycol VMA, vanilmandelic acid...

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