Bisulfite treatment? - (Apr/27/2006 )

So I was posed a question today in my lab meeting and realized I wasn't sure what the answer was.

How is it that sodium bisulfite treatment doesn't affect 5mC? Since the sulphonation step occurs at the 6 carbon position of the ring, is it steric hindrance from the methyl group that results in the inability for the SO3- group to attach hence stopping the reaction? Or is some other mechanism involved?

i recall very vaguely, that the sulphonation step is an SN2 reaction that occurs on unmethylated cytosines in the given pH and reaction conditions, the SN2 reaction can not occur as well when the 5' carbon is methylated.

I could be wrong on this one though, as it was a very vague memory. *sigh* i miss my organic chem.

Nick