Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “MANDELIC ACID”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,243 records · Page 69Linked to original sources
PubMed1969

Dopamine (3-hydroxytyramine) metabolism in parkinsonism.

Three patients with idiopathic parkinsonism and six normal subjects were infused over a 4 hr period with 104.6 muc of dopamine-2-(14)C (3,4-dihydroxyphenylethylamine, 3-hydroxytyramine),(1) the immediate precursor in the synthesis of the sympathetic neurohormone, noradrenaline (norepinephrine). Urine was collected during the infusion period, 0-2 hr, 2-4 hr, 4-8 hr, 8-24 hr, and thereafter for 4 additional days. Using a technique herein described, the various metabolic and biosynthetic products of dopamine, including noradrenaline and its metabolic products, were separated, identified, and their radioactivity measured. The metabolic pattern of dopamine in the normal subject was compared to that of the three parkinsonism patients. The results indicate that in idiopathic parkinsonism there is a decrease in the recovery of free radioactive noradrenaline in the urine following an infusion of dopamine-2-(14)C and a slight shift toward dopamine metabolism. The latter is reflected by an increase in the following metabolites of dopamine: 3,4-dihydroxyphenylacetic acid and the conjugates of 3-methoxy-4-hydroxyphenylacetic acid, 3,4-dihydroxyphenylacetic acid, 3-methoxy-4-hydroxyphenylethanol and dopamine.

Adult↗
PubMed2006

Accelerating unimolecular decarboxylation by preassociated acid catalysis in thiamin-derived intermediates: implicating Brønsted acids as carbanion traps in enzymes.

Mandelylthiamin (MT) is formally the conjugate of thiamin and benzoylformate. It is the simplified analogue of the first covalent intermediate in benzoylformate decarboxylase. Although MT is the functional equivalent of the enzymic intermediate, it is 106-fold less reactive in decarboxylation. Furthermore, upon loss of carbon dioxide, it undergoes a fragmentation reaction that is about 102-fold faster than the enzymic reaction. While Brønsted acids in general can suppress the fragmentation to some extent, they do not accelerate the decarboxylation. Surprisingly, the conjugate acid of pyridine accelerates decarboxylation; it also blocks fragmentation with particularly high efficiency. These results are consistent with the conjugate acid of pyridine acting as a "spectator" catalyst, associating with MT prior to decarboxylation. In the absence of catalyst, carbon dioxide formed upon carbon-carbon bond breaking overwhelmingly reverts to the carboxylate. Association of pyridine (and its conjugate acid) with MT permits trapping of the nascent carbanion by protonation, while nonassociated acids must arrive by the relatively slow process of diffusion. C-Alkyl pyridine acids provide similar catalysis while other acids have no effect. This suggests that an enzyme that generates an aldehyde from a 2-ketoacid should have functional Brønsted acids in their active sites that would trap the carbanion, as does benzoylformate decarboxylase. Enzymes that give nonaldehydic products from decarboxylation of thiamin diphosphate conjugates containing an associated electron acceptor or electrophilic substrate would also be able to prevent the reversal of decarboxylation.

Acids↗