a 6-O-methyl-2'-deoxyguanosine in DNA + L-cysteinyl-[protein] = a 2'-deoxyguanosine in DNA + S-methyl-L-cysteinyl-[protein] a 4-O-methyl-thymidine in DNA + L-cysteinyl-[protein] = a thymidine in DNA + S-methyl-L-cysteinyl-[protein] This enzyme catalyzes only one turnover and therefore is not strictly catalytic. According to one definition, an enzyme is a biocatalyst that acts repeatedly and over many reaction cycles. Belongs to the MGMT family.