Fluorometric assay of rat tissue N-methyltransferases with nicotinamide and four isomeric methylnicotinamides.
Nicotinamide (NA) and its four isomeric methyl analogs [2-, 4-, 5- and 6-methylnicotinamides (MNs)] were tested as substrates for nicotinamide N-methyltransferase (NNMT) and amine N-methyltransferase (ANMT) using rat liver, kidney, spleen and brain 9000 x g supernatant fluids as model enzyme preparations. The N-methylated products were determined fluorometrically by their reaction with acetophenone or 4-methoxybenzaldehyde to form fluorescent 2,7-naphthyridine derivatives, and the lower limits of the determination were 8-30 pmol/100 microliters. N-Methyltransferase activities were detected in the liver with NA, 4-MN and 5-MN, and in the brain and spleen with 4-MN. On this basis, 5-MN is considered to be a selective substrate for NNMT in addition to NA, which is a known methyl acceptor for this enzyme. Although 4-MN appears to serve as a methyl acceptor for both ANMT and NNMT, it seems to be essentially a selective substrate for brain ANMT because of the absence of NNMT in brain. The fluorometric methods used here are also very useful because of their simplicity, sensitivity and selectivity.
Sano
A
A
Faculty of Pharmaceutical Sciences, Science University of Tokyo, Japan.
Endo
N
N
Takitani
S
S
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D005470:Fluorometry; D066298:In Vitro Techniques; D008297:Male; D008780:Methyltransferases / Q000032:analysis* / Q000378:metabolism; D009536:Niacinamide / Q000031:analogs & derivatives / Q000494:pharmacology*; D050903:Nicotinamide N-Methyltransferase; D051381:Rats; D011919:Rats, Inbred Strains
D009536:Niacinamide; D008780:Methyltransferases; C494406:NNMT protein, human; D050903:Nicotinamide N-Methyltransferase; C008472:N-methylnicotinamide