N-methylation of biogenic amines. I. Characterization and properties of an N-methyltransferase in rat brain using 5-methyltetrahydrofolic acid as the methyl donor

Metabolism of phenylethanolamines and 2-oxo-2-phenylethylamines in the rat

1. The metabolism of a series of phenylethanolamines and 2-oxo-2-phenylethylamines was examined in vivo in the rat. 2. The urinary excretion of the corresponding mandelic acids was, in general, considerably greater for 2-oxo-2-phenylethylamines than for the corresponding phenylethanolamines. Of the putative metabolites of the former class of compounds only phenylglyoxals yielded mandelic acids.

Dementia-peripheral neuropathy during combined deficiency of vitamin B12 and folate. Light microscopy and ultrastructural study of sural nerve

We present a case of a 56 year old woman who, in consequence of repeated surgical resections of the small bowel, developed a slowly progressive and mainly motor polyneuropathy affecting the lower limbs. The polyneuropathy due to a combined deficiency of vitamin B12 and folate, was associated with intellectual deterioration, involving especially the mnesic functions. Light microscopy and ultrastructural study of sural nerve revealed: marked reduction of every order of myelinated fibers: aspects of wallerian-like myelin degeneration; various stages of myelin leaflet delamination into the cytoplasm of Schwann cells and/or macrophages; lack of alterations attributable to a primary axonal degeneration. The morphological results suggest a primary demyelination, followed secondarily by either axonal changes or some aspects of wallerian-like degeneration.

Lack of epinine formation in adrenal medulla and brain of rats during cold exposure and inhibition of dopamine beta-hydroxylase

Cold exposure of rats for 4 h and simultaneous inhibition of dopamine beta-hydroxylase by FLA-63 (25mg/kg) led to a reduction of the catecholamine content of the adrenal medulla by 46% and of the brain by 68%. Additional injections of 5 mg/kg FLA-63 4 and 9 h after beginning of the experiments, respectively, kept the catecholamine content on this low level (brain) or decreased it further (adrenal medulla). Administration of 5 mg/kg (-)DOPA together with the mono-amine oxidase inhibitor pargyline (50 mg/kg) 24 h after the first injection of FLA-63 stimulated the resynthesis. It amounted for the adrenal medulla to 20 mug/kg body weight/8 h and for the brain to 45ng/g tissue wet weight/8 h. Paper chromatographic analyses of the extracts of adrenal medulla and brain, respectively, performed at each time of the different injections, clearly identified adrenaline, noradrenaline and dopamine (in traces) in the adrenal medulla as well as noradrenaline and dopamine in the brain; epinine on the contray could not be demonstrated, not even in traces. Since at least 25 ng of epinine can be detected with certainty by our method, it can be concluded that epinine is not formed in amounts greater than 75 ng/pair adrenal glands or 37.5 ng/brain. The present results support the view that the main pathway of adrenaline biosynthesis in the suprarenal medulla and the brain proceeds via noradrenaline and not via epinine.

Tissue fractionation in rat brain, kidney and liver. I. Intracellular localization of a 5-methyltetrahydrofolic acid requiring enzyme

The intracellular distribution of N-methyl-transferase requiring 5-methyl-tetrahydrofolic acid (5 MT-NMT) was studied in brain, kidney and liver of rats. Among these different tissues, the kidney displayed the highest enzyme activity, more than 20 times the activity detected in the brain. As the striatum and, to a lesser extent the hypothalamus, were found to contain slightly higher 5 MT-NMT than other cerebral regions, they were also selected for the study of the subcellular localization. Tissue fractionation was performed by differential centrifugation yielding five different fractions which were analyzed for their enzymatic content not only of 5 MT-NMT but also of marker enzymes, such as cytochrome oxidase, acid phosphatase and inosine diphosphatase. In all the tissues studied, 5 MT-NMT was recovered in the supernatant fraction. Therefore one may consider this enzyme to belong to the cytosol. Although a neuronal localization cannot be excluded, it is beyond doubt that the enzyme is contained in other cellular types. In the brain fractionation, the five fraction procedure seems to be very useful especially when the subcellular distribution of a given enzyme is compared to that obtained in other tissues like liver or kidney. Finally 5 MT-NMT may be considered a good marker enzyme for the supernatant fraction.

Identification of alkaloids; the condensation products of biogenic amines with formaldehyde, enzymatically formed from 5-methyltetrahydrofolic acid

The use of thin-layer chromatography has demonstrated that incubations of indoleamines with 5-methyl[14-C]tetrahydrofolic acid and an enzyme previously described as an N-methyltransferase, do not yield Nw, N1, or O-methylated products. Further elucidation by thin-layer chromatography, gas chromatography, mass spectrometry and selected ion monitoring enabled us to identify the reaction products as tetrahydroisoquinolines and tetrahydro-beta-carbolines in mixtures incubated respectively with catecholamines and indoleamines in the presence of 5-methyl[14-C]tetrahydrofolic acid and enzyme. The alkaloids have been shown to originate from a spontaneous condensation of the corresponding amines with formaldehyde, this latter being formed in the first stage of the reaction by enzymatic conversion from 5-methyltetrahydrofolic acid.

5-methyltetrahydrofolic acid is not a methyl donor for biogenic amines: enzymatic formation of formaldehyde

Contrary to previous reports, 5-methyltetrahydrofolic acid does not mediate the methylation of dopamine to epinine. Instead, this methyl donor is degraded enzymatically to formaldehyde, which condenses with dopamine to form a tetahydoisoquinoline derivative. The latter has chromotographic characteristics very similar to those of epinine, which likely accounts for the original misidentification of the product.

Ontogenetic development of a 5-methyltetrahydrofolate requiring enzyme in rats and mice

Developmental characteristics of 5-methyltetrahydrofolate requiring N-methyltransferase (5 MT-NMT) have been studied in rats and mice and compared to the development pattern of marker enzymes. In rat and mouse brain, the 5 MT-NMT activity expressed in units per mg protein, was found to decrease rapidly during the first five days after birth and then more slowly, whereas two other enzymes, dopa-decarboxylase and histamine N-methyltransferase increased gradually during maturation. In kidney, the ontogenetic development of 5 MT-NMT was first characterized by an increasing activity from birth until a different age, depending on the species, and then followed by an abrupt decline. In contrast to this, histamine N-methyltransferase activity in mouse kidney was about 60 times higher at maturity than at birth. When the enzyme activities are expressed in units per g tissue, the changes in the course of the development of 5 MT-NMT were less apparent, but in any way differed markedly from those of dopa-decarboxylase and histamine N-methyltransferase. The results suggest that 5 MT-NMT does not behave as a synaptosomal or perhaps even as a neuronal enzyme. Although its physiological role remains to be elucidated, it must have a more general function in the cellular economy than merely N-methylating biogenic amines.

5-Methyltetrahydrofolic Acid as a Mediator in the Formation of Pyridoindoles

Enzymes from chick and rat tissues catalyze the reaction of N-methyl tryptamine with 5-methyltetrahydrofolic acid to form 2,3,4,9-tetrahydro-2-methyl-1H-pyrido[3,4b] indole. N,N-Dimethyltryptamine was not formed. With tryptamine as substrate the product is 2,3,4,9-tetrahydro-1H-pyrido[3,4b] indole and not N-methyltryptamine. These pyridoindoles were not formed when S-adenosylmethionine was cosubstrare.