Regional formation of 6-methoxy-1,2,3,4-tetrahydro-beta-carboline in rat brain extract

In the presence of 5-methoxytryptamine (5-MeOT), 5-methyltetrahydrofolic acid (5-MTHF) yields 6-methoxy-1,2,3,4-tetrahydro-beta-carboline (6-MeOTHbetaC) in rat brain extracts, possibly via formaldehyde formation catalyzed by methylenetetrahydrofolate reductase. The formation of 6-MeOTHbetaC in selected brain regions, ranging from 452 +/- 40 pmol formed per mg protein per hour in corpus striatum to 119 +/- 17 pmol in cingulate cortex, is significantly correlated with the regional distribution of 1,2,3,4-tetrahydro-beta-carboline (THbetaC) formed from 5-MTHF and tryptamine (r = 0.76, p less than 0.01) as well as that of methylene-beta-phenylethylimine (MbetaphiEI) from 5-MTHF and beta-phenylethylamine (betaphiEA; r = 0.90, p less than 0.01). FAD enhances the activity, lowering both Vmax and Km values with respect to 5-MeOT and Vmax, but not Km, with respect to 5-MTHF.