[The kinetic mechanism of phage T4 DNA-[N6-adenine]-methyltransferase].
Kinetic analysis of methyl group transfer from S-adenosyl-L-methionine (SAM) to the GATC recognition site catalyzed by the phage T4 DNA-[N6-adenine]-methyltransferase (MTase) [EC 2.1.1.72] showed that the reverse reaction is at least 500 times slower than the direct one. The overall pattern of product inhibition corresponds to an ordered steady-state mechanism following the sequence SAM decreases DNA decreases metDNA increases SAH increases (S-adenosyl-L-homocysteine). Pronounced inhibition was observed at high concentrations of the 20-meric substrate duplex, which may be attributed to formation of a dead-end complex MTase-SAH-DNA. In contrast, high SAM concentrations proportionally accelerated the reaction. Thus, the reaction may include a stage whereby the binding of SAM and the release of SAH are united into one concerted event. Computer fitting of alternative kinetic schemes to the aggregate of experimental data revealed that the most plausible mechanism involves isomerization of the enzyme.
Evdokimov
A A
AA
Institute of Molecular Biology, State Research Center for Virology and Biotechnology VECTOR, Kol'tsovo, Novosibirsk Region, 633159 Russia.
Zinov'ev
V V
VV
Malygin
E G
EG
D017122:Bacteriophage T4 / Q000201:enzymology*; D007700:Kinetics; D008956:Models, Chemical; D009692:Nucleic Acid Heteroduplexes; D012435:S-Adenosylhomocysteine / Q000737:chemistry / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000737:chemistry / Q000378:metabolism; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific) / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*
D009692:Nucleic Acid Heteroduplexes; D012436:S-Adenosylmethionine; D012435:S-Adenosylhomocysteine; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific)