[New studies on inhibition of tRNA N2 guanine methyltransferase by S-adenosyl-homocysteine and S-adenosyl-methionine analogs].

New structural analogs of S-adenosyl homocysteine (SAH) 1-9, 11-14, 19-21) and of S-adenosyl methionine (15-18) have been tested as inhibitors of a N-2 guanine methyltransferase extract from rabbit liver with E. coli B tRNA as substrate. The sulfonium compounds (mixture of +/- diastereoisomers) are more inhibitory than the sulfide derivatives but less inhibitory than SAH itself. The replacement of the aminoacid chain in SAH by various alphatic radicals leads to a correlation between their bulk and the size of the enzymatic site. The monosubstitution of N-6 amino group does not affect significantly the inhibitory effect, which is completely canceled by the disubstitution of N-6.