2-Methyladenosine (methyl-
Ado) has selective activity against Mycobacterium tuberculosis (M.
tuberculosis). In an effort to better understand its mechanism of action, we have characterized its metabolism in M.
tuberculosis cells. The primary intracellular metabolite of methyl-
Ado was 2-methyl-adenylate (methyl-
AMP). Very little of the methyl-
AMP was metabolized further. A M.
tuberculosis strain that was resistant to methyl-
Ado did not express
adenosine kinase and did not convert methyl-
Ado to methyl-
AMP in intact cells. In contrast to these results, the primary intracellular metabolite of
adenosine in M.
tuberculosis cells was
ATP, which was readily incorporated into
RNA. The rate of metabolism of methyl-
Ado to methyl-
AMP was similar to the rate of metabolism of
adenosine to
ATP. Treatment of M.
tuberculosis with methyl-
Ado did not affect intracellular
ATP levels. Methyl-
Ado and
Ado were also cleaved to
2-methyladenine and
adenine, respectively, which accumulated in the medium outside the cells. These studies suggested that methyl-
AMP was the active metabolite responsible for the cytotoxicity of this agent. Furthermore, because methyl-
Ado was poorly metabolized in human cells, these studies indicated that the selective activity of methyl-
Ado was due to its selective activation by M.
tuberculosis. These studies have identified two
enzyme reactions (
Ado kinase and
Ado cleavage) in M.
tuberculosis that could be exploited for the rational design of new and selective anti-M.
tuberculosis agents.