[Effect of S-nucleosyl-L-homocysteines on the activity of DNA methylases].

It was studied effect of S-adenosyl, -uridyl, -citidyl and -inosyl homocysteines on activity of bacterial adenine and cytosine methylases from E. coli CK as well as on guanine methylase specific for DDVI phage. S-adenosyl homocysteine was shown to be the strong inhibitor of methylation; 10 micrometer of the substance inhibited all the enzymes studied by 98--99%. Use of total enzymatic preparations did not enable to find a difference in affinity of S-uridyl, -citidyl, and -inosyl homocysteines to various DNA methylases studied. All these preparations inhibited DNA methylases by 55--65%. Increase in concentration of inhibitor up to 20 micrometer did not elevate the inhibitory effect. Action of S-nucleosyl homocysteines did not depend on the type of acceptory DNA.