Adenosine kinase (AK) is a purine salvage enzyme that catalyzes the phosphorylation of adenosine to AMP. In Mycobacterium tuberculosis, AK can also catalyze the phosphorylation of the adenosine analog 2-methyladenosine (methyl-Ado), the first step in the metabolism of this compound to an active form. Purification of AK from M. tuberculosis yielded a 35-kDa protein that existed as a dimer in its native form. Adenosine (Ado) was preferred as a substrate at least 30-fold (K m ‫؍‬ 0.8 ؎ 0.08 M) over other natural nucleosides, and substrate inhibition was observed when Ado concentrations exceeded 5 M. M. tuberculosis and human AKs exhibited different affinities for methyl-Ado, with K m values of 79 and 960 M, respectively, indicating that differences exist between the substrate binding sites of these enzymes. ATP was a good phosphate donor (K m ‫؍‬ 1100 ؎ 140 M); however, the activity levels observed with dGTP and GTP were 4.7 and 2.5 times the levels observed with ATP, respectively. M. tuberculosis AK activity was dependent on Mg 2؉ , and activity was stimulated by potassium, as reflected by a decrease in the K m and an increase in V max for both Ado and methyl-Ado. The N-terminal amino acid sequence of the purified enzyme revealed complete identity with Rv2202c, a protein currently classified as a hypothetical sugar kinase. When an AK-deficient strain of M. tuberculosis (SRICK1) was transformed with this gene, it exhibited a 5,000-fold increase in AK activity compared to extracts from the original mutants. These results verified that the protein that we identified as AK was coded for by Rv2202c. AK is not commonly found in bacteria, and to the best of our knowledge, M. tuberculosis AK is the first bacterial AK to be characterized. The enzyme shows greater sequence homology with ribokinase and fructokinase than it does with other AKs. The multiple differences that exist between M. tuberculosis and human AKs may provide the molecular basis for the development of nucleoside analog compounds with selective activity against M. tuberculosis.

Objective We assessed the efficacy of a maternal multi–dose azithromycin (AZI) regimen, with and without anti–inflammatory agents to delay preterm birth and to mitigate fetal lung injury associated with Ureaplasma parvum intra–amniotic infection (IAI). Study Design Long–term catheterized rhesus monkeys (n=16) received intra–amniotic inoculation of U. parvum (107 CFU/ml, serovar 1). After contraction onset, rhesus monkeys received either no treatment (n=6); AZI (12.5mg/kg, q12h, IV for 10 days; n=5); or AZI plus dexamethasone (DEX) and indomethacin (INDO; n=5). Outcomes included amniotic fluid pro–inflammatory mediators, U. parvum cultures & PCR, AZI pharmacokinetics and the extent of fetal lung inflammation. Results Maternal AZI therapy eradicated U. parvum IAI from the amniotic fluid within 4 days. Placenta and fetal tissues were 90% culture negative at delivery. AZI therapy significantly delayed preterm delivery and prevented advanced fetal lung injury, although residual acute chorioamnionitis persisted. Conclusions Specific maternal antibiotic therapy can eradicate U. parvum from the amniotic fluid and key fetal organs, with subsequent prolongation of pregnancy which provides a therapeutic window of opportunity to effectively reduce the severity of fetal lung injury.

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Our study demonstrates that a maternal multiple-dose AZI regimen is effective in eradicating U. parvum IAI by virtue of intra-amniotic accumulation and suggests that antenatal therapy has the potential to mitigate complications associated with U. parvum infection in pregnancy, such as preterm labor and fetal sequelae.