Evidence that xylosyladenine affects methylation by inhibition of S-adenosyl-L-methionine synthesis.

The adenosine analogs, 9-beta-D-xylofuranosyladenine (XA) and 3'-deoxyadenosine (cordycepin) were tested for their ability to interfer with S-adenosyl-L-methionine (SAM) formation in L1210 cells in vitro. XA inhibited the incorporation of [3H]methionine into SAM in a mixed-competitive manner, while cordycepin was not inhibitory. The adenosine deaminase inhibitor, 2-deoxy-coformycin produced a marked potentiation of the inhibitory effect of XA on Sam synthesis, but did not affect the inactivity of cordycepin. These results indicate that the inhibitory action of XA, but not cordycepin, on the methylation of nuclear RNA may be attributed to interference with the synthesis of SAM.