An endogenous inhibitor of indoleamine-N-methyltransferase in cerebrospinal fluid

Naturally occurring methylation inhibitor: DNA hypomethylation and hemoglobin synthesis in human K562 cells

A naturally occurring methylation inhibitor isolated from rabbit liver and named methinin inhibits a number of methyltransferases. Methinin is a low-molecular-weight compound (1,400) that has an active amine group. This compound inhibits the DNA methyltransferase of human erythroleukemia cells (K562) in vitro. When the K562 cells were grown in medium containing methinin, fetal hemoglobin was produced. Small but detectable amounts of adult hemoglobin were also produced. Methinin was not toxic to these cells. The overall rate of genomic DNA methylation was reduced by 60% in cells grown in medium containing methinin. Southern blots of genomic DNA from methinin-treated cells and untreated cells hybridized to a 32P-labeled globin gene probe showed that one site in the globin gene region was hypomethylated. Methinin is a naturally occurring compound which inhibits DNA methylation both in vitro and in vivo.

Naturally occurring methylation inhibitor: DNA hypomethylation and hemoglobin synthesis in human K562 cells

A naturally occurring methylation inhibitor isolated from rabbit liver and named methinin inhibits a number of methyltransferases. Methinin is a low-molecular-weight compound (1,400) that has an active amine group. This compound inhibits the DNA methyltransferase of human erythroleukemia cells (K562) in vitro. When the K562 cells were grown in medium containing methinin, fetal hemoglobin was produced. Small but detectable amounts of adult hemoglobin were also produced. Methinin was not toxic to these cells. The overall rate of genomic DNA methylation was reduced by 60% in cells grown in medium containing methinin. Southern blots of genomic DNA from methinin-treated cells and untreated cells hybridized to a 32P-labeled globin gene probe showed that one site in the globin gene region was hypomethylated. Methinin is a naturally occurring compound which inhibits DNA methylation both in vitro and in vivo.

N-methylation and quaternization of pyridine in vitro by rabbit lung, liver and kidney N-methyltransferases: an S-adenosyl-L-methionine-dependent reaction

The N-methylation of pyridine in vitro, using dialysed and undialysed hepatic, pulmonary, renal and brain preparations from rabbits, is described. Analysis of the quaternary metabolite, N-methylpyridinium ion, was carried out by selective ion-pair extraction and cation-exchange high-performance liquid chromatography (h.p.l.c.) using a u.v. detector, and also by direct cation-exchange h.p.l.c. of incubates containing S-adenosyl-L-[methyl-3H]methionine using a flow-through radioactivity detector. N-Methylation of pyridine could be readily demonstrated with dialysed homogenates, 9000 g and 100 000 g supernatant fractions from lung, kidney and liver, but not with any of the brain preparations. 'Pyridine N-methyltransferase' activity was confined to the tissue cytosol, and this enzyme utilized S-adenosyl-L-methionine as the methyl donor. Since the activity of the 'pyridine N-methyltransferase' in rabbit tissues is increased many fold by dialysis, this enzyme, in common with most other N-methylating enzymes, is subject to inhibition by a low-molecular-weight endogenous substance.