Tryptophan lyase (NosL) is a radical S-adenosyl-L-methionine (SAM) enzyme that catalyzes the formation of 3-methyl-2-indolic acid from L-tryptophan. In this paper, we demonstrate that the S'-deoxyadenosyl radical is considerably more versatile in its chemistry than previously anticipated: hydrogen atom abstraction from N-alpha-cydopropyltryptophan occurs at C alpha rather than the amino group with NosL Y90A and replacing the substrate amine with a ketone or an alkene changes the chemistry from hydrogen atom abstraction to double bond addition. In addition, the 5'-deoxyadenosyl radical can add to the [4Fe-4S] cluster and dithionite can be used to trap radicals at the active site.